dev-lisp/gcl: build w/ -std=gnu17

We already have a bunch of other workarounds piled up here.

Closes: https://bugs.gentoo.org/947758
Signed-off-by: Sam James <sam@gentoo.org>

dev-lisp/gcl/gcl-2.6.13_pre99.ebuild

@@ -1,4 +1,4 @@
-# Copyright 1999-2024 Gentoo Authors
+# Copyright 1999-2025 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=7
@@ -34,6 +34,7 @@ PATCHES=(
 src_configure() {
 	filter-lto # bug #931082
 	strip-flags
+	append-cflags -std=gnu17 # bug #947758
 	filter-flags -fstack-protector -fstack-protector-all
 	# breaks linking on multiple defined syms
 	#append-cflags $(test-flags-CC -fgnu89-inline)

dev-lisp/gcl/gcl-2.6.14.ebuild

@@ -29,6 +29,7 @@ DEPEND="${RDEPEND}
 src_configure() {
 	filter-lto # bug #931082
 	strip-flags
+	append-cflags -std=gnu17 # bug #947758
 	filter-flags -fstack-protector -fstack-protector-all
 	# breaks linking on multiple defined syms
 	#append-cflags $(test-flags-CC -fgnu89-inline)

dev-lisp/gcl/gcl-2.6.15_pre3.ebuild

@@ -37,6 +37,7 @@ S="${WORKDIR}"/${PN}-Version_2_6_15pre3/${PN}
 src_configure() {
 	filter-lto # bug #931082
 	strip-flags
+	append-cflags -std=gnu17 # bug #947758
 	filter-flags -fstack-protector -fstack-protector-all
 
 	local tcl=""