Merge branch 'rh/autoconf-rhel3'

Build update for older RHEL.

* rh/autoconf-rhel3:
  configure.ac: check for HMAC_CTX_cleanup
  configure.ac: check for clock_gettime and CLOCK_MONOTONIC
  configure.ac: check 'tv_nsec' field in 'struct stat'

git-compat-util.h

@@ -218,6 +218,9 @@ extern char *gitbasename(char *);
 #include <openssl/err.h>
 #undef MAC_OS_X_VERSION_MIN_REQUIRED
 #undef __AVAILABILITY_MACROS_USES_AVAILABILITY
+#ifdef NO_HMAC_CTX_CLEANUP
+#define HMAC_CTX_cleanup HMAC_cleanup
+#endif
 #endif
 
 /* On most systems <netdb.h> would have given us this, but