Don't re-define strlcpy/strlcat with >=glibc-2.38

`>=glibc-2.38` implements strlcpy, strlcat, etc so check for those functions
with Meson and don't provide conflicting prototypes.

Technically, it doesn't need _GNU_SOURCE, but it's easier because it's not
clear right now what glibc wants to guard it with. Note that these are in
POSIX next anyway.

Fixes: https://github.com/OpenRC/openrc/issues/643
Signed-off-by: Sam James <sam@gentoo.org>

meson.build

@@ -203,6 +203,10 @@ if cc.has_function('close_range', prefix: '#define _GNU_SOURCE\n#include <unistd
   add_project_arguments('-DHAVE_CLOSE_RANGE_CLOEXEC', language: 'c')
 endif
 
+if cc.has_function('strlcpy', prefix: '#define _GNU_SOURCE\n#include <string.h>')
+  add_project_arguments('-DHAVE_STRLCPY', language: 'c')
+endif
+
 incdir = include_directories('src/shared')
 einfo_incdir = include_directories('src/libeinfo')
 rc_incdir = include_directories('src/librc')

src/libeinfo/libeinfo.c

@@ -146,9 +146,7 @@ static const char *const color_terms[] = {
 };
 #endif
 
-/* strlcat and strlcpy are nice, shame glibc does not define them */
-#ifdef __GLIBC__
-#  if !defined (__UCLIBC__) && !defined (__dietlibc__)
+#ifndef HAVE_STRLCPY
 static size_t
 strlcat(char *dst, const char *src, size_t size)
 {
@@ -177,7 +175,6 @@ strlcat(char *dst, const char *src, size_t size)
 	return dst_n + (s - src);
 }
 #endif
-#endif
 
 static bool
 yesno(const char *value)

src/shared/helpers.h

@@ -37,11 +37,9 @@
 
 #define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
 
-#ifdef __GLIBC__
-#  if !defined (__UCLIBC__) && !defined (__dietlibc__)
+#ifndef HAVE_STRLCPY
 #    define strlcpy(dst, src, size) snprintf(dst, size, "%s", src)
 #endif
-#endif
 
 #ifndef timespecsub
 #define	timespecsub(tsp, usp, vsp)					      \