wrapper: add xgetcwd()

Add the helper function xgetcwd(), which returns the current directory
or dies.  The returned string has to be free()d after use.

Helped-by: Duy Nguyen <pclouds@gmail.com>
Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -538,6 +538,7 @@ extern int xmkstemp(char *template);
 extern int xmkstemp_mode(char *template, int mode);
 extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
 extern int odb_pack_keep(char *name, size_t namesz, const unsigned char *sha1);
+extern char *xgetcwd(void);
 
 static inline size_t xsize_t(off_t len)
 {

wrapper.c

@@ -493,3 +493,11 @@ struct passwd *xgetpwuid_self(void)
 		    errno ? strerror(errno) : _("no such user"));
 	return pw;
 }
+
+char *xgetcwd(void)
+{
+	struct strbuf sb = STRBUF_INIT;
+	if (strbuf_getcwd(&sb))
+		die_errno(_("unable to get current working directory"));
+	return strbuf_detach(&sb, NULL);
+}