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/mutex.m4
+++ b/dist/aclocal/mutex.m4
@@ -3,8 +3,9 @@
 # POSIX pthreads tests: inter-process safe and intra-process only.
 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;
@@ -24,6 +25,7 @@ main() {
 	pthread_mutexattr_destroy(&mutexattr));
 }], [db_cv_mutex="$1"],,
 AC_TRY_LINK([
+#include <stdlib.h>
 #include <pthread.h>],[
 	pthread_cond_t cond;
 	pthread_mutex_t mutex;
@@ -45,8 +47,9 @@ AC_TRY_LINK([
 ], [db_cv_mutex="$1"]))])
 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;
@@ -64,6 +67,7 @@ main() {
 	pthread_mutexattr_destroy(&mutexattr));
 }], [db_cv_mutex="$1"],,
 AC_TRY_LINK([
+#include <stdlib.h>
 #include <pthread.h>],[
 	pthread_cond_t cond;
 	pthread_mutex_t mutex;
@@ -158,6 +162,7 @@ if test "$db_cv_mutex" = no; then
 	# LWP threads: _lwp_XXX
 	if test "$db_cv_mutex" = no; then
 	AC_TRY_LINK([
+	#include <stdlib.h>
 	#include <synch.h>],[
 		static lwp_mutex_t mi = SHAREDMUTEX;
 		static lwp_cond_t ci = SHAREDCV;
@@ -174,6 +179,7 @@ if test "$db_cv_mutex" = no; then
 	LIBS="$LIBS -lthread"
 	AC_TRY_LINK([
 	#include <thread.h>
+	#include <stdlib.h>
 	#include <synch.h>],[
 		mutex_t mutex;
 		cond_t cond;
@@ -189,6 +195,7 @@ if test "$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;
@@ -213,7 +220,7 @@ if test "$db_cv_mutex" = no; then
 	# x86/gcc: FreeBSD, NetBSD, BSD/OS, Linux
 	AC_TRY_COMPILE(,[
 	#if (defined(i386) || defined(__i386__)) && defined(__GNUC__)
-		exit(0);
+		return 0;
 	#else
 		FAIL TO COMPILE/LINK
 	#endif
@@ -222,7 +229,7 @@ if test "$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
@@ -245,7 +252,7 @@ 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
@@ -287,7 +294,7 @@ 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
@@ -304,7 +311,7 @@ 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
 
@@ -326,7 +333,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__USLC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -383,7 +390,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__alpha) && defined(__DECC)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -394,7 +401,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__alpha) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -405,7 +412,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__arm__) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -416,7 +423,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(__mips) || defined(__mips__)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -427,7 +434,7 @@ fi
 if test "$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
@@ -438,7 +445,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if (defined(__powerpc__) || defined(__ppc__)) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -449,7 +456,7 @@ fi
 if test "$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
@@ -460,7 +467,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__MVS__) && defined(__IBMC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -471,7 +478,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__s390__) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -482,7 +489,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(__ia64) && defined(__GNUC__)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -493,7 +500,7 @@ fi
 if test "$db_cv_mutex" = no; then
 AC_TRY_COMPILE(,[
 #if defined(_UTS)
-	exit(0);
+	return 0;
 #else
 	FAIL TO COMPILE/LINK
 #endif
@@ -814,9 +821,9 @@ 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
@@ -825,6 +832,7 @@ 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@:>@;