Simplify strchrnul() compat code

strchrnul() was introduced in glibc in April 1999 and included in
glibc-2.1. Checking for that version means the majority of all git
users would get to use the optimized version in glibc. Of the
remaining few some might get to use a slightly slower version
than necessary but probably not slower than what we have today.

Unfortunately, __GLIBC_PREREQ() macro was not available in glibc 2.1.1
which was short lived but already supported strchrnul().  Odd minority
users of that library needs to live with our compatibility inline version.

Rediffed-against-next-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-compat-util.h b/git-compat-util.h
index e72654b..92d7967 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -183,9 +183,14 @@
                 const void *needle, size_t needlelen);
 #endif
 
-#ifdef NO_STRCHRNUL
+#if !defined(__GLIBC_PREREQ) && !__GLIBC_PREREQ(2, 1)
 #define strchrnul gitstrchrnul
-char *gitstrchrnul(const char *s, int c);
+static inline char *gitstrchrnul(const char *s, int c)
+{
+	while (*s && *s != c)
+		s++;
+	return (char *)s;
+}
 #endif
 
 extern void release_pack_memory(size_t, int);