grep: create a "is_fixed" member in "grep_pat"

This change paves the way for later using this value the regex compile
functions themselves.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

grep.c

@@ -606,7 +606,6 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 {
 	int err;
 	int regflags = REG_NEWLINE;
-	int pat_is_fixed;
 
 	p->word_regexp = opt->word_regexp;
 	p->ignore_case = opt->ignore_case;
@@ -615,11 +614,11 @@ static void compile_regexp(struct grep_pat *p, struct grep_opt *opt)
 	if (memchr(p->pattern, 0, p->patternlen) && !opt->pcre2)
 		die(_("given pattern contains NULL byte (via -f <file>). This is only supported with -P under PCRE v2"));
 
-	pat_is_fixed = is_fixed(p->pattern, p->patternlen);
-	if (p->fixed || pat_is_fixed) {
+	p->is_fixed = is_fixed(p->pattern, p->patternlen);
+	if (p->fixed || p->is_fixed) {
 #ifdef USE_LIBPCRE2
 		opt->pcre2 = 1;
-		if (pat_is_fixed) {
+		if (p->is_fixed) {
 			compile_pcre2_pattern(p, opt);
 		} else {
 			/*

grep.h

@@ -88,6 +88,7 @@ struct grep_pat {
 	pcre2_compile_context *pcre2_compile_context;
 	uint32_t pcre2_jit_on;
 	unsigned fixed:1;
+	unsigned is_fixed:1;
 	unsigned ignore_case:1;
 	unsigned word_regexp:1;
 };