https://bugs.gentoo.org/879857
https://github.com/Perl/perl5/commit/e1ca9a418fa6b7d26fbb1931c9164141035262c3
https://github.com/Perl/perl5/commit/fc35cee89c1a42558f50a37a6b4d5186b77f058b

From e1ca9a418fa6b7d26fbb1931c9164141035262c3 Mon Sep 17 00:00:00 2001
From: Peter Levine <plevine457@gmail.com>
Date: Tue, 17 Jan 2023 02:47:12 -0500
Subject: [PATCH] Add parameter types to declarations for clang-16

ANSI C style function declarations without parameter types are errors with clang-16.
--- a/Configure
+++ b/Configure
@@ -7927,10 +7927,10 @@ $cat >malloc.c <<END
 #include <stdlib.h>
 #endif
 #ifdef TRY_MALLOC
-void *malloc();
+void *malloc(size_t);
 #endif
 #ifdef TRY_FREE
-void free();
+void free(void *);
 #endif
 END
 case "$malloctype" in

From fc35cee89c1a42558f50a37a6b4d5186b77f058b Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 17 Jan 2023 19:07:54 +0100
Subject: [PATCH] Configure: Add various C99 compatibility improvements

Two C99 compatibility issues are fixed by these changes: Return
types are made explicit where they previously defaulted to int,
and all called functions are now declared explicitly (either by
including additional headers, or by adding prototypes manually).

This avoids implict ints and implicit function declarations,
both legacy C language features removed in the 1999 revision
of the language.

Verified with an instrumented GCC compiler on GNU/Linux.
--- a/Configure
+++ b/Configure
@@ -4655,7 +4655,7 @@ esac
 # so we will take those off from locincpth.
 case "$gccversion" in
 3.*)
-    echo "main(){}">try.c
+    echo "int main(){}">try.c
     for incdir in $locincpth; do
        warn=`$cc $ccflags -I$incdir -c try.c 2>&1 | \
 	     grep '^c[cp]p*[01]: warning: changing search order '`
@@ -5798,6 +5798,7 @@ case "$intsize" in
 #ifdef I_STDLIB
 #include <stdlib.h>
 #endif
+#include <stdio.h>
 int main()
 {
 	printf("intsize=%d;\n", (int)sizeof(int));
@@ -6871,6 +6872,7 @@ case "$doublesize" in
 #ifdef I_STDLIB
 #include <stdlib.h>
 #endif
+#include <stdio.h>
 int main()
 {
     printf("%d\n", (int)sizeof(double));
@@ -12660,7 +12662,7 @@ case "$dlsrc" in
 dl_dlopen.xs)
 	echo "Checking whether your dlsym() needs a leading underscore ..." >&4
 	$cat >dyna.c <<'EOM'
-fred () { }
+void fred (void) { }
 EOM
 
 $cat >fred.c<<EOM
@@ -12679,7 +12681,7 @@ $cat >fred.c<<EOM
 #include <link.h>
 #endif
 
-extern int fred() ;
+extern void fred(void) ;
 
 int main()
 {
@@ -13713,6 +13715,7 @@ $cat >try.c <<EOP
 #ifdef I_STDLIB
 #include <stdlib.h>
 #endif
+#include <string.h>
 #define FILE_ptr(fp)	$stdio_ptr
 #define FILE_cnt(fp)	$stdio_cnt
 int main() {
@@ -16220,6 +16223,7 @@ echo "Checking to see if your libm supports _LIB_VERSION..." >&4
 $cat >try.c <<EOCP
 #include <unistd.h>
 #include <math.h>
+#include <stdio.h>
 int main (int argc, char *argv[])
 {
     printf ("%d\n", _LIB_VERSION);
@@ -22168,13 +22172,15 @@ pager="$ans"
 : see if ar generates random libraries by itself
 echo " "
 echo "Checking how to generate random libraries on your machine..." >&4
-echo 'int bar1() { return bar2(); }' > bar1.c
+echo 'extern int bar2(); int bar1() { return bar2(); }' > bar1.c
 echo 'int bar2() { return 2; }' > bar2.c
 $cat > foo.c <<EOP
 #$i_stdlib I_STDLIB
 #ifdef I_STDLIB
 #include <stdlib.h>
 #endif
+#include <stdio.h>
+extern int bar1();
 int main() { printf("%d\n", bar1()); exit(0); }
 EOP
 $cc $ccflags -c bar1.c >/dev/null 2>&1
@@ -22400,7 +22406,7 @@ EOM
 			for nfd in 'int' 'size_t' 'unsigned long' 'unsigned' ; do
 				for tmo in 'struct timeval *' 'const struct timeval *'; do
 					case "$val" in
-					'')	try="$extern_C select _(($nfd, $xxx, $xxx, $xxx, $tmo));"
+					'')	try="$extern_C int select _(($nfd, $xxx, $xxx, $xxx, $tmo));"
 						if ./protochk "$try" $hdrs; then
 							echo "Your system accepts $xxx."
 							val="$xxx"