git-compat-util.h: Honor HP C's noreturn attribute

HP C for Integrity servers (Itanium) gained support for noreturn
attribute sometime in 2006. It was released in Compiler Version
A.06.10 and made available in July 2006.

The __HP_cc define detects the HP C compiler version.  Precede the
__GNUC__ check so it works well when compiling with HP C using -Agcc
option that enables partial support for the GNU C dialect. The -Agcc
defines the __GNUC__ too.

Signed-off-by: Michal Rokos <michal.rokos@nextsoft.cz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -208,7 +208,10 @@ extern char *gitbasename(char *);
 #define is_dir_sep(c) ((c) == '/')
 #endif
 
-#ifdef __GNUC__
+#if __HP_cc >= 61000
+#define NORETURN __attribute__((noreturn))
+#define NORETURN_PTR
+#elif defined(__GNUC__)
 #define NORETURN __attribute__((__noreturn__))
 #define NORETURN_PTR __attribute__((__noreturn__))
 #elif defined(_MSC_VER)