tools/perf: Turn strlcpy() into a __weak function

The strlcpy() feature check slows every build unnecessarily - so make it
a __weak function so it does not have to be auto-detected.

If the libc (or any other library) has an strlcpy() implementation it will
be used - otherwise our fallback is active.

Cc: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Link: http://lkml.kernel.org/n/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

tools/perf/config/Makefile

···
 	libperl				\
 	libpython			\
 	libpython-version		\
-	strlcpy				\
 	libbfd				\
 	on-exit				\
 	backtrace			\
···
         endif
       endif
     endif
-  endif
-endif
-
-ifndef NO_STRLCPY
-  ifeq ($(feature-strlcpy), 1)
-    CFLAGS += -DHAVE_STRLCPY_SUPPORT
   endif
 endif
 

tools/perf/config/feature-checks/Makefile

···
 	test-libperl			\
 	test-libpython			\
 	test-libpython-version		\
-	test-strlcpy			\
 	test-libbfd			\
 	test-on-exit			\
 	test-backtrace			\
···
 
 test-libpython-version:
 	$(BUILD) $(FLAGS_PYTHON_EMBED)
-
-test-strlcpy:
-	$(BUILD)
 
 test-libbfd:
 	$(BUILD) -DPACKAGE='perf' -DPACKAGE=perf -lbfd -ldl

tools/perf/config/feature-checks/test-strlcpy.c

···
-#include <stdlib.h>
-extern size_t strlcpy(char *dest, const char *src, size_t size);
-
-int main(void)
-{
-	strlcpy(NULL, NULL, 0);
-	return 0;
-}

tools/perf/util/cache.h

···
 extern char *perf_pathdup(const char *fmt, ...)
 	__attribute__((format (printf, 1, 2)));
 
-#ifndef HAVE_STRLCPY_SUPPORT
+/* Matches the libc/libbsd function attribute so we declare this unconditionally: */
 extern size_t strlcpy(char *dest, const char *src, size_t size);
-#endif
 
 #endif /* __PERF_CACHE_H */

tools/perf/util/include/linux/compiler.h

···
 # define __force
 #endif
 
+#ifndef __weak
+# define __weak			__attribute__((weak))
+#endif
+
 #endif

tools/perf/util/path.c

···
 	return ".";
 }
 
-#ifndef HAVE_STRLCPY_SUPPORT
-size_t strlcpy(char *dest, const char *src, size_t size)
+/*
+ * If libc has strlcpy() then that version will override this
+ * implementation:
+ */
+size_t __weak strlcpy(char *dest, const char *src, size_t size)
 {
 	size_t ret = strlen(src);
 
 	if (size) {
 		size_t len = (ret >= size) ? size - 1 : ret;
+
 		memcpy(dest, src, len);
 		dest[len] = '\0';
 	}
+
 	return ret;
 }
-#endif
 
 static char *get_pathname(void)
 {