sys-apps/ed: build w/ -std=gnu17 (for now)

It's already been reported upstream (thank you!) and the next release
should work. Added a TODO to drop the hack then.

Closes: https://bugs.gentoo.org/943764
Signed-off-by: Sam James <sam@gentoo.org>

sys-apps/ed/ed-1.20.2.ebuild

@@ -38,8 +38,9 @@ src_unpack() {
 }
 
 src_configure() {
+	# TOOD: -std=gnu99 can be dropped on next release > 1.20.2
 	edo ./configure \
-		CC="$(tc-getCC)" \
+		CC="$(tc-getCC) -std=gnu99" \
 		CFLAGS="${CFLAGS}" \
 		LDFLAGS="${LDFLAGS}" \
 		CPPFLAGS="${CPPFLAGS}" \