glibc: don't ignore global LDFLAGS settings

Two things: The -Wl,-rpath-link comment is stale (due to per-recipe
staging), so we no longer need to set our own LDFLAGS to avoid
-Wl,-rpath-link being in there. Second, overriding LDFLAGS should be
done at the recipe level so "bitbake -e" can show what is going on.
Otherwise debugging why one's global LDFLAGS tweaks are being ignored
is needlessly painful.

So pull out the LDFLAGS setting from do_compile, and change it to an
append instead of assignment.

For the benefit of future git blame: the -fuse-ld=bfd setting was
added by ac64c3b96b (glibc: always use bfd linker).

(From OE-Core rev: 4535469d5953b94c9dcad5515be9b807ea7ba621)

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/glibc/glibc_2.31.bb

@@ -91,9 +91,8 @@ do_configure () {
         CPPFLAGS="" oe_runconf
 }
 
+LDFLAGS += "-fuse-ld=bfd"
 do_compile () {
-	# -Wl,-rpath-link <staging>/lib in LDFLAGS can cause breakage if another glibc is in staging
-	LDFLAGS="-fuse-ld=bfd"
 	base_do_compile
 	echo "Adjust ldd script"
 	if [ -n "${RTLDLIST}" ]