ksh: use _GNU_SOURCE on musl only.

srcpkgs/ksh/template

@@ -2,7 +2,7 @@
 pkgname=ksh
 version=2012.08.01
 _debpkgver=93u+20120801
-revision=3
+revision=4
 wrksrc=${pkgname}-${_debpkgver}
 register_shell="/bin/ksh"
 short_desc="AT&T's Korn shell (ksh93)"
@@ -17,6 +17,7 @@ build_options="static"
 
 case "$XBPS_TARGET_MACHINE" in
 *-musl)
+CFLAGS='-D_GNU_SOURCE'
 post_extract() {
 	# Don't rewrite xxx64 to xxx.
 	sed -i '/define.*off_t/d' src/lib/libast/include/ast_std.h
@@ -38,12 +39,10 @@ do_build() {
 	if [ "$build_option_static" ]; then
 		LDFLAGS+=" -static"
 	fi
-	echo $CC
 	export SHELL=/bin/sh    # bin/package breaks on bash
 	$SHELL bin/package make \
 		CC="${CC}" LDFLAGS="${LDFLAGS}" \
-		CFLAGS="${CFLAGS} -D_GNU_SOURCE" \
-		CCFLAGS="${CFLAGS} -D_GNU_SOURCE" \
+		CFLAGS="${CFLAGS}" CCFLAGS="${CFLAGS}" \
 		HOSTTYPE="$($SHELL bin/package host canon $XBPS_CROSS_TRIPLET)"
 }