Define compat version of mkdtemp for systems lacking it

Solaris 9 doesn't have mkdtemp() so we need to emulate it for the
rsync transport implementation.  Since Solaris 9 is lacking this
function we can also reasonably assume it is not available on
Solaris 8 either.  The new Makfile definition NO_MKDTEMP can be
set to enable the git compat version.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

git-compat-util.h

@@ -147,6 +147,11 @@ extern ssize_t git_pread(int fd, void *buf, size_t count, off_t offset);
 extern int gitsetenv(const char *, const char *, int);
 #endif
 
+#ifdef NO_MKDTEMP
+#define mkdtemp gitmkdtemp
+extern char *gitmkdtemp(char *);
+#endif
+
 #ifdef NO_UNSETENV
 #define unsetenv gitunsetenv
 extern void gitunsetenv(const char *);