[gcc r13-6888] fixincludes: Declare memmem if it's not declared in system headers [PR109293]

[gcc r13-6888] fixincludes: Declare memmem if it's not declared in system headers [PR109293]

[Xi Ruoyao]

https://gcc.gnu.org/g:21c74b6ea41d21ef96813b34bfa55c51a82d6c99

commit r13-6888-g21c74b6ea41d21ef96813b34bfa55c51a82d6c99
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Tue Mar 28 01:48:02 2023 +0800

    fixincludes: Declare memmem if it's not declared in system headers [PR109293]
    
    memmem is not POSIX so the system may lack it.  Then libiberty will
    provide an implementation, but it's a "supplemental function" and not
    declared in libiberty.h.  We need to declare the prototype to use it
    then.
    
    See libiberty doc at
    https://gcc.gnu.org/onlinedocs/libiberty/Supplemental-Functions.html.
    
    Tested by bootstrapping GCC in the following container environments on
    x86_64-linux-gnu:
    
    1. "Vanilla" system with memmem in Glibc.
    2. memmem removed from string.h.
    3. memmem removed from both string.h and libc.so.
    
    For 3, also verified that memmem from libiberty is linked into fixincl
    executable.
    
    Ok for trunk?
    
    fixincludes/ChangeLog:
    
            PR other/109293
            * configure.ac (AC_CHECK_DECLS): Add memmem.
            * configure: Regenerate.
            * config.h.in: Regenerate.
            * system.h (memmem): Declare if HAVE_DECL_MEMMEM is zero.

Diff:
---
 fixincludes/config.h.in  |  4 ++++
 fixincludes/configure    | 10 ++++++++++
 fixincludes/configure.ac |  2 +-
 fixincludes/system.h     |  4 ++++
 4 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/fixincludes/config.h.in b/fixincludes/config.h.in
index 69a67f5f116..0fd21b721b9 100644
--- a/fixincludes/config.h.in
+++ b/fixincludes/config.h.in
@@ -78,6 +78,10 @@
    don't. */
 #undef HAVE_DECL_GETC_UNLOCKED
 
+/* Define to 1 if you have the declaration of `memmem', and to 0 if you don't.
+   */
+#undef HAVE_DECL_MEMMEM
+
 /* Define to 1 if you have the declaration of `putchar_unlocked', and to 0 if
    you don't. */
 #undef HAVE_DECL_PUTCHAR_UNLOCKED
diff --git a/fixincludes/configure b/fixincludes/configure
index b3bca666a4d..bdcc41f6ddc 100755
--- a/fixincludes/configure
+++ b/fixincludes/configure
@@ -5043,6 +5043,16 @@ fi
 cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_VASPRINTF $ac_have_decl
 _ACEOF
+ac_fn_c_check_decl "$LINENO" "memmem" "ac_cv_have_decl_memmem" "$ac_includes_default"
+if test "x$ac_cv_have_decl_memmem" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_MEMMEM $ac_have_decl
+_ACEOF
 
 ac_fn_c_check_decl "$LINENO" "clearerr_unlocked" "ac_cv_have_decl_clearerr_unlocked" "$ac_includes_default"
 if test "x$ac_cv_have_decl_clearerr_unlocked" = xyes; then :
diff --git a/fixincludes/configure.ac b/fixincludes/configure.ac
index 14813b910f1..ef2227e3c93 100644
--- a/fixincludes/configure.ac
+++ b/fixincludes/configure.ac
@@ -88,7 +88,7 @@ define(fixincludes_UNLOCKED_FUNCS, clearerr_unlocked feof_unlocked dnl
   fread_unlocked fwrite_unlocked getchar_unlocked getc_unlocked dnl
   putchar_unlocked putc_unlocked)
 AC_CHECK_FUNCS(fixincludes_UNLOCKED_FUNCS)
-AC_CHECK_DECLS([abort, asprintf, basename(char *), errno, vasprintf])
+AC_CHECK_DECLS([abort, asprintf, basename(char *), errno, vasprintf, memmem])
 AC_CHECK_DECLS(m4_split(m4_normalize(fixincludes_UNLOCKED_FUNCS)))
 
 # Checks for typedefs, structures, and compiler characteristics.
diff --git a/fixincludes/system.h b/fixincludes/system.h
index dca5d57b2e3..687fb2e2025 100644
--- a/fixincludes/system.h
+++ b/fixincludes/system.h
@@ -209,6 +209,10 @@ extern int errno;
 extern void abort (void);
 #endif
 
+#if defined (HAVE_DECL_MEMMEM) && !HAVE_DECL_MEMMEM
+extern void *memmem (const void *, size_t, const void *, size_t);
+#endif
+
 #if HAVE_SYS_STAT_H
 # include <sys/stat.h>
 #endif