Makefile: use compat regex on IRIX 6.5

The IRIX 6.5 regex.h header file defines REG_STARTEND, but the feature does
not appear to work.  Since REG_STARTEND is required for proper functioning
of git-grep, set NO_REGEX and use the alternative regex libraries in compat/

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -982,6 +982,7 @@ ifeq ($(uname_S),IRIX)
 	# NO_MMAP.  If you suspect that your compiler is not affected by this
 	# issue, comment out the NO_MMAP statement.
 	NO_MMAP = YesPlease
+	NO_REGEX = YesPlease
 	SNPRINTF_RETURNS_BOGUS = YesPlease
 	SHELL_PATH = /usr/gnu/bin/bash
 	NEEDS_LIBGEN = YesPlease
@@ -1000,6 +1001,7 @@ ifeq ($(uname_S),IRIX64)
 	# NO_MMAP.  If you suspect that your compiler is not affected by this
 	# issue, comment out the NO_MMAP statement.
 	NO_MMAP = YesPlease
+	NO_REGEX = YesPlease
 	SNPRINTF_RETURNS_BOGUS = YesPlease
 	SHELL_PATH=/usr/gnu/bin/bash
 	NEEDS_LIBGEN = YesPlease