https://bugs.gentoo.org/883413
--- a/dist/aclocal/clock.m4
+++ b/dist/aclocal/clock.m4
@@ -20,12 +20,14 @@ esac
 #	existence to mean the clock really exists.
 AC_CACHE_CHECK([for clock_gettime monotonic clock], db_cv_clock_monotonic, [
 AC_TRY_RUN([
+#include <time.h>
 #include <sys/time.h>
-main() {
+int main(void) {
 	struct timespec t;
 	return (clock_gettime(CLOCK_MONOTONIC, &t) != 0);
 }], db_cv_clock_monotonic=yes, db_cv_clock_monotonic=no,
 AC_TRY_LINK([
+#include <time.h>
 #include <sys/time.h>], [
 struct timespec t;
 clock_gettime(CLOCK_MONOTONIC, &t);
--- a/dist/aclocal/mmap.m4
+++ b/dist/aclocal/mmap.m4
@@ -28,8 +28,10 @@ if test "$mmap_ok" = "yes" ; then
     /* Not all these includes are needed, but the minimal set varies from
      * system to system.
      */
+    #include <stdlib.h>
     #include <stdio.h>
     #include <string.h>
+    #include <unistd.h>
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <fcntl.h>
@@ -42,13 +44,12 @@ if test "$mmap_ok" = "yes" ; then
     #define MAP_FAILED (-1)
     #endif
 
-    int catch_sig(sig)
-	    int sig;
+    void catch_sig(int sig)
     {
 	    exit(1);
     }
 
-    main() {
+    int main(void) {
 	    const char *underlying;
 	    unsigned gapsize;
 	    char *base;
--- a/dist/aclocal/mutex.m4
+++ b/dist/aclocal/mutex.m4
@@ -5,7 +5,7 @@ AC_DEFUN(AM_PTHREADS_SHARED, [
 AC_TRY_RUN([
 #include <stdlib.h>
 #include <pthread.h>
-main() {
+int main(void) {
 	pthread_cond_t cond;
 	pthread_mutex_t mutex;
 	pthread_condattr_t condattr;
@@ -49,7 +49,7 @@ AC_DEFUN(AM_PTHREADS_PRIVATE, [
 AC_TRY_RUN([
 #include <stdlib.h>
 #include <pthread.h>
-main() {
+int main(void) {
 	pthread_cond_t cond;
 	pthread_mutex_t mutex;
 	pthread_condattr_t condattr;
@@ -89,7 +89,7 @@ AC_DEFUN(AM_PTHREADS_CONDVAR_DUPINITCHK, [
 AC_TRY_RUN([
 #include <stdlib.h>
 #include <pthread.h>
-main() {
+int main(void) {
 	pthread_cond_t cond;
 	pthread_condattr_t condattr;
 	exit(pthread_condattr_init(&condattr) ||
@@ -110,7 +110,7 @@ AC_DEFUN(AM_PTHREADS_RWLOCKVAR_DUPINITCHK, [
 AC_TRY_RUN([
 #include <stdlib.h>
 #include <pthread.h>
-main() {
+int main(void) {
 	pthread_rwlock_t rwlock;
 	pthread_rwlockattr_t rwlockattr;
 	exit(pthread_rwlockattr_init(&rwlockattr) ||
@@ -227,6 +227,7 @@ if test "$db_cv_mutex" = no; then
 	# LWP threads: _lwp_XXX
 	if test "$db_cv_mutex" = no; then
 	AC_TRY_LINK([
+	#include <stdlib.h>
 	#include <synch.h>],[
 		static lwp_mutex_t mi = SHAREDMUTEX;
 		static lwp_cond_t ci = SHAREDCV;
@@ -243,6 +244,7 @@ if test "$db_cv_mutex" = no; then
 	LIBS="$LIBS -lthread"
 	AC_TRY_LINK([
 	#include <thread.h>
+	#include <stdlib.h>
 	#include <synch.h>],[
 		mutex_t mutex;
 		cond_t cond;
@@ -258,6 +260,7 @@ if test "$db_cv_mutex" = no; then
 	if test "$db_cv_mutex" = no -o "$db_cv_mutex" = ui_only; then
 	AC_TRY_LINK([
 	#include <thread.h>
+	#include <stdlib.h>
 	#include <synch.h>],[
 		mutex_t mutex;
 		cond_t cond;
@@ -282,7 +285,7 @@ if test "$db_cv_mutex" = no; then
 	# x86/gcc: FreeBSD, NetBSD, BSD/OS, Linux
 	AC_TRY_COMPILE(,[
 	#if (defined(i386) || defined(__i386__)) && defined(__GNUC__)
-		exit(0);
+		return 0;
 	#else
 		FAIL TO COMPILE/LINK
 	#endif
@@ -291,7 +294,7 @@ if test "$db_cv_mutex" = no; then
 	# x86_64/gcc: FreeBSD, NetBSD, BSD/OS, Linux
 	AC_TRY_COMPILE(,[
 	#if (defined(x86_64) || defined(__x86_64__)) && defined(__GNUC__)
-		exit(0);
+		return 0;
 	#else
 		FAIL TO COMPILE/LINK
 	#endif
@@ -314,7 +317,7 @@ if test "$db_cv_mutex" = no; then
 	AC_TRY_COMPILE(,[
 	#if defined(__sparc__) && defined(__GNUC__)
 		asm volatile ("membar #StoreStore|#StoreLoad|#LoadStore");
-		exit(0);
+		return 0;
 	#else
 		FAIL TO COMPILE/LINK
 	#endif
@@ -356,7 +359,7 @@ AC_TRY_LINK([
 	msem_init(&x, 0);
 	msem_lock(&x, 0);
 	msem_unlock(&x, 0);
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -373,7 +376,7 @@ AC_TRY_LINK([
 	msem_init(&x, 0);
 	msem_lock(&x, 0);
 	msem_unlock(&x, 0);
-	exit(0);
+	return 0;
 ], [db_cv_mutex=UNIX/msem_init])
 fi
 
@@ -395,7 +398,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__USLC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -452,7 +455,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__alpha) && defined(__DECC)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -463,7 +466,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__alpha) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -474,7 +477,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__arm__) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -485,7 +488,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(__mips) || defined(__mips__)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -496,7 +499,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(__hppa) || defined(__hppa__)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -507,7 +510,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(__powerpc__) || defined(__ppc__)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -518,7 +521,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(mc68020) || defined(sun3)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -529,7 +532,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__MVS__) && defined(__IBMC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -540,7 +543,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__s390__) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -551,7 +554,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__ia64) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -562,7 +565,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(_UTS)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -910,9 +913,9 @@ fi
 if test "$db_cv_atomic" = no; then
 	AC_TRY_COMPILE(,[
 	#if ((defined(i386) || defined(__i386__)) && defined(__GNUC__))
-		exit(0);
+		return 0;
 	#elif ((defined(x86_64) || defined(__x86_64__)) && defined(__GNUC__))
-		exit(0);
+		return 0;
 	#else
 		FAIL TO COMPILE/LINK
 	#endif
@@ -921,6 +924,7 @@ fi
 
 if test "$db_cv_atomic" = no; then
 AC_TRY_LINK([
+#include <stdlib.h>
 #include <sys/atomic.h>],[
 	volatile unsigned val = 1;
 	exit (atomic_inc_uint_nv(&val) != 2 ||
--- a/dist/aclocal/sequence.m4
+++ b/dist/aclocal/sequence.m4
@@ -43,7 +43,9 @@ AC_DEFUN(AM_SEQUENCE_CONFIGURE, [
 	# test, which won't test for the appropriate printf format strings.
 	if test "$db_cv_build_sequence" = "yes"; then
 		AC_TRY_RUN([
-		main() {
+		#include <stdio.h>
+		#include <string.h>
+		int main(void) {
 			$db_cv_seq_type l;
 			unsigned $db_cv_seq_type u;
 			char buf@<:@100@:>@;
@@ -59,7 +61,10 @@ AC_DEFUN(AM_SEQUENCE_CONFIGURE, [
 				return (1);
 			return (0);
 		}],, [db_cv_build_sequence="no"],
-		AC_TRY_LINK(,[
+		AC_TRY_LINK([
+		#include <stdio.h>
+		#include <string.h>
+		],[
 			$db_cv_seq_type l;
 			unsigned $db_cv_seq_type u;
 			char buf@<:@100@:>@;
--- a/dist/aclocal/types.m4
+++ b/dist/aclocal/types.m4
@@ -69,7 +69,7 @@ AC_SUBST(stdint_h_decl)
 AC_MSG_CHECKING(for stdint.h)
 AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 #include <stdint.h>
-  int main() {
+  int main(void) {
   uint_least8_t x=0;
   return x;
   }])],[AC_MSG_RESULT(yes)
@@ -77,7 +77,7 @@ if test "$db_cv_cxx" = "yes"; then
   AC_MSG_CHECKING([if stdint.h can be used by C++])
   AC_LANG_PUSH(C++)
   AC_COMPILE_IFELSE([AC_LANG_SOURCE([#include <stdint.h>
-    int main() {
+    int main(void) {
     uint_least8_t x=0;
     return x;
   }])],[AC_MSG_RESULT(yes)