Revert "builtin-grep: workaround for non GNU grep."

This reverts 518920b7 commit.
Linus has a more portable alternative.

Makefile

@@ -46,8 +46,6 @@ all:
 #
 # Define NO_MMAP if you want to avoid mmap.
 #
-# Define NO_H_OPTION_IN_GREP if your grep does not understand -H.
-#
 # Define WITH_OWN_SUBPROCESS_PY if you want to use with python 2.3.
 #
 # Define NO_IPV6 if you lack IPv6 support and getaddrinfo().
@@ -446,12 +444,6 @@ ifdef NO_ACCURATE_DIFF
 	ALL_CFLAGS += -DNO_ACCURATE_DIFF
 endif
 
-ifdef NO_H_OPTION_IN_GREP
-	NO_H_OPTION_IN_GREP=1
-else
-	NO_H_OPTION_IN_GREP=0
-endif
-
 # Shell quote (do not use $(call) to accomodate ancient setups);
 
 SHA1_HEADER_SQ = $(subst ','\'',$(SHA1_HEADER))
@@ -534,9 +526,6 @@ git$X git.spec \
 %.o: %.S
 	$(CC) -o $*.o -c $(ALL_CFLAGS) $<
 
-builtin-grep.o: builtin-grep.c
-	$(CC) -o $*.o -c $(ALL_CFLAGS) -DNO_H_OPTION_IN_GREP=$(NO_H_OPTION_IN_GREP) $<
-
 exec_cmd.o: exec_cmd.c
 	$(CC) -o $*.o -c $(ALL_CFLAGS) '-DGIT_EXEC_PATH="$(gitexecdir_SQ)"' $<
 

builtin-grep.c

@@ -453,6 +453,7 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 
 	len = nr = 0;
 	push_arg("grep");
+	push_arg("-H");
 	if (opt->fixed)
 		push_arg("-F");
 	if (opt->linenum)
@@ -502,13 +503,7 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 		push_arg("-e");
 		push_arg(p->pattern);
 	}
-
-	if (NO_H_OPTION_IN_GREP)
-		push_arg("/dev/null");
-	else {
-		push_arg("-H");
-		push_arg("--");
-	}
+	push_arg("--");
 
 	hit = 0;
 	argc = nr;
@@ -540,19 +535,8 @@ static int grep_cache(struct grep_opt *opt, const char **paths, int cached)
 	 * Use the external "grep" command for the case where
 	 * we grep through the checked-out files. It tends to
 	 * be a lot more optimized
-	 *
-	 * Some grep implementations do not understand -H nor --
-	 * but /dev/null can be used as a substitution in most
-	 * cases.
-	 *
-	 * However -L and -c would slightly misbehave (-L would
-	 * list /dev/null as a hit, and -c would report 0 hits
-	 * from /dev/null); so do not use the external one on
-	 * such platforms.
 	 */
-	if (!cached &&
-	    (!NO_H_OPTION_IN_GREP ||
-	     (!opt->count && !opt->unmatch_name_only))) {
+	if (!cached) {
 		hit = external_grep(opt, paths, cached);
 		if (hit >= 0)
 			return hit;