https://bugs.gentoo.org/870412
https://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=8b5e2016c7ed2d67f31b03a3d2e361858ff5299b

Backport the K&R decls fix to 2.71 to avoid configure tests
failing (often "silently", i.e. doesn't fail the build of
the package overall, just leads to wrong results) with
newer compilers like the upcoming Clang 16.

From 8b5e2016c7ed2d67f31b03a3d2e361858ff5299b Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 1 Sep 2022 16:19:50 -0500
Subject: Port to compilers that moan about K&R func decls
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* lib/autoconf/c.m4 (AC_LANG_CALL, AC_LANG_FUNC_LINK_TRY):
Use '(void)' rather than '()' in function prototypes, as the latter
provokes fatal errors in some compilers nowadays.
* lib/autoconf/functions.m4 (AC_FUNC_STRTOD):
* tests/fortran.at (AC_F77_DUMMY_MAIN usage):
* tests/semantics.at (AC_CHECK_DECLS):
Don’t use () in a function decl.
--- a/lib/autoconf/c.m4
+++ b/lib/autoconf/c.m4
@@ -133,7 +133,7 @@ m4_if([$2], [main], ,
 #ifdef __cplusplus
 extern "C"
 #endif
-char $2 ();])], [return $2 ();])])
+char $2 (void);])], [return $2 ();])])
 
 
 # AC_LANG_FUNC_LINK_TRY(C)(FUNCTION)
@@ -157,7 +157,7 @@ m4_define([AC_LANG_FUNC_LINK_TRY(C)],
 #define $1 innocuous_$1
 
 /* System header to define __stub macros and hopefully few prototypes,
-   which can conflict with char $1 (); below.  */
+   which can conflict with char $1 (void); below.  */
 
 #include <limits.h>
 #undef $1
@@ -168,7 +168,7 @@ m4_define([AC_LANG_FUNC_LINK_TRY(C)],
 #ifdef __cplusplus
 extern "C"
 #endif
-char $1 ();
+char $1 (void);
 /* The GNU C library defines this for functions which it implements
     to always fail with ENOSYS.  Some functions are actually named
     something starting with __ and the normal name is an alias.  */
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -1613,9 +1613,6 @@ AC_DEFUN([AC_FUNC_STRTOD],
 AC_CACHE_CHECK(for working strtod, ac_cv_func_strtod,
 [AC_RUN_IFELSE([AC_LANG_SOURCE([[
 ]AC_INCLUDES_DEFAULT[
-#ifndef strtod
-double strtod ();
-#endif
 int
 main (void)
 {
--- a/tests/fortran.at
+++ b/tests/fortran.at
@@ -233,7 +233,7 @@ void FOOBAR_F77 (double *x, double *y);
 #  ifdef __cplusplus
      extern "C"
 #  endif
-   int F77_DUMMY_MAIN () { return 1; }
+   int F77_DUMMY_MAIN (void) { return 1; }
 #endif
 
 int main(int argc, char *argv[])
@@ -315,7 +315,7 @@ void FOOBAR_FC(double *x, double *y);
 #  ifdef __cplusplus
      extern "C"
 #  endif
-   int FC_DUMMY_MAIN () { return 1; }
+   int FC_DUMMY_MAIN (void) { return 1; }
 #endif
 
 int main (int argc, char *argv[])
@@ -561,7 +561,7 @@ void @foobar@ (int *x);
 #  ifdef __cplusplus
      extern "C"
 #  endif
-   int F77_DUMMY_MAIN () { return 1; }
+   int F77_DUMMY_MAIN (void) { return 1; }
 #endif
 
 int main(int argc, char *argv[])
@@ -637,7 +637,7 @@ void @foobar@ (int *x);
 #  ifdef __cplusplus
      extern "C"
 #  endif
-   int FC_DUMMY_MAIN () { return 1; }
+   int FC_DUMMY_MAIN (void) { return 1; }
 #endif
 
 int main(int argc, char *argv[])
--- a/tests/semantics.at
+++ b/tests/semantics.at
@@ -207,7 +207,7 @@ AT_CHECK_MACRO([AC_CHECK_DECLS],
 		 [[extern int yes;
 		   enum { myenum };
 		   extern struct mystruct_s { int x[20]; } mystruct;
-		   extern int myfunc();
+		   extern int myfunc (int);
 		   #define mymacro1(arg) arg
 		   #define mymacro2]])
   # Ensure we can detect missing declarations of functions whose
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