tools lib string: Adopt prefixcmp() from perf and subcmd

Both had copies originating from git.git, move those to
tools/lib/string.c, getting both tools/lib/subcmd/ and tools/perf/ to
use it.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-uidwtticro1qhttzd2rkrkg1@git.kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>

tools/include/linux/string.h

@@ -18,4 +18,6 @@ extern size_t strlcpy(char *dest, const char *src, size_t size);
 
 char *str_error_r(int errnum, char *buf, size_t buflen);
 
+int prefixcmp(const char *str, const char *prefix);
+
 #endif /* _LINUX_STRING_H_ */

tools/lib/string.c

@@ -87,3 +87,12 @@ size_t __weak strlcpy(char *dest, const char *src, size_t size)
 	}
 	return ret;
 }
+
+int prefixcmp(const char *str, const char *prefix)
+{
+	for (; ; str++, prefix++)
+		if (!*prefix)
+			return 0;
+		else if (*str != *prefix)
+			return (unsigned char)*prefix - (unsigned char)*str;
+}

tools/lib/subcmd/help.c

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <linux/string.h>
 #include <termios.h>
 #include <sys/ioctl.h>
 #include <sys/types.h>

tools/lib/subcmd/parse-options.c

 #include <linux/compiler.h>
+#include <linux/string.h>
 #include <linux/types.h>
 #include <stdio.h>
 #include <stdlib.h>

tools/lib/subcmd/subcmd-util.h

@@ -79,13 +79,4 @@ static inline void astrcat(char **out, const char *add)
 	free(tmp);
 }
 
-static inline int prefixcmp(const char *str, const char *prefix)
-{
-	for (; ; str++, prefix++)
-		if (!*prefix)
-			return 0;
-		else if (*str != *prefix)
-			return (unsigned char)*prefix - (unsigned char)*str;
-}
-
 #endif /* __SUBCMD_UTIL_H */

tools/perf/util/strbuf.c

@@ -3,15 +3,6 @@
 #include <linux/kernel.h>
 #include <errno.h>
 
-int prefixcmp(const char *str, const char *prefix)
-{
-	for (; ; str++, prefix++)
-		if (!*prefix)
-			return 0;
-		else if (*str != *prefix)
-			return (unsigned char)*prefix - (unsigned char)*str;
-}
-
 /*
  * Used as the default ->buf value, so that people can always assume
  * buf is non NULL and ->buf is NUL terminated even for a freshly

tools/perf/util/util.h

@@ -30,8 +30,6 @@ void warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
 
 void set_warning_routine(void (*routine)(const char *err, va_list params));
 
-int prefixcmp(const char *str, const char *prefix);
-
 static inline void *zalloc(size_t size)
 {
 	return calloc(1, size);