perl: enable _GNU_SOURCE define via d_gnulibc

This is needed to properly support memmem() and friends under musl
as musl guards the declarations with _GNU_SOURCE define, and if the
declarations are not present, gcc will issue warnings and generate
assembly that assumes the functions return int (instead of e.g.
void*), with catastrophic consequences at runtime.

(From OE-Core rev: 79dc3f42958bfefe03a8240e2a57501c38d2bd3c)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 6422e62fbc5c65a2165a72c97c880cfa9a80e957)
Signed-off-by: Peter Hurley <peter@meraki.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/recipes-devtools/perl/perl_5.34.3.bb

@@ -70,6 +70,7 @@ do_configure:class-target() {
     -Dlibpth='${libdir} ${base_libdir}' \
     -Dglibpth='${libdir} ${base_libdir}' \
     -Alddlflags=' ${LDFLAGS}' \
+    -Dd_gnulibc=define \
     ${PACKAGECONFIG_CONFARGS}
 
     #perl.c uses an ARCHLIB_EXP define to generate compile-time code that