grep/pcre2: use pcre2_maketables_free() function

Make use of the pcre2_maketables_free() function to free the memory
allocated by pcre2_maketables().

At first sight it's strange that 10da030ab7 (grep: avoid leak of
chartables in PCRE2, 2019-10-16) which added the free() call here
doesn't make use of the pcre2_free() the author introduced in the
preceding commit in 513f2b0bbd (grep: make PCRE2 aware of custom
allocator, 2019-10-16).

The reason is that at the time the function didn't exist. It was first
introduced in PCREv2 version 10.34, released on 2019-11-21.

Let's make use of it behind a macro. I don't think this matters for
anything to do with custom allocators, but it makes our use of PCREv2
more discoverable.

At some distant point in the future we'll be able to drop the version
guard, as nobody will be running a version older than 10.34.

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

grep.c

@@ -490,7 +490,11 @@ static void free_pcre2_pattern(struct grep_pat *p)
 	pcre2_compile_context_free(p->pcre2_compile_context);
 	pcre2_code_free(p->pcre2_pattern);
 	pcre2_match_data_free(p->pcre2_match_data);
+#ifdef GIT_PCRE2_VERSION_10_34_OR_HIGHER
+	pcre2_maketables_free(pcre2_global_context, p->pcre2_tables);
+#else
 	free((void *)p->pcre2_tables);
+#endif
 }
 #else /* !USE_LIBPCRE2 */
 static void compile_pcre2_pattern(struct grep_pat *p, const struct grep_opt *opt)

grep.h

@@ -7,6 +7,9 @@
 #if (PCRE2_MAJOR >= 10 && PCRE2_MINOR >= 36) || PCRE2_MAJOR >= 11
 #define GIT_PCRE2_VERSION_10_36_OR_HIGHER
 #endif
+#if (PCRE2_MAJOR >= 10 && PCRE2_MINOR >= 34) || PCRE2_MAJOR >= 11
+#define GIT_PCRE2_VERSION_10_34_OR_HIGHER
+#endif
 #else
 typedef int pcre2_code;
 typedef int pcre2_match_data;