dev-scheme/guile: build 3.0.10-r102 w/ -std=gnu17

The fix from bug #944029 seems insufficient and master has changed
a fair bit so I've not gone through commits to see if it's fixed there
yet.

Bug: https://bugs.gentoo.org/943712
Closes: https://bugs.gentoo.org/944029
Signed-off-by: Sam James <sam@gentoo.org>

dev-scheme/guile/guile-3.0.10-r102.ebuild

@@ -3,7 +3,7 @@
 
 EAPI=8
 
-inherit autotools
+inherit autotools flag-o-matic
 
 DESCRIPTION="GNU Ubiquitous Intelligent Language for Extensions"
 HOMEPAGE="https://www.gnu.org/software/guile/"
@@ -64,6 +64,9 @@ src_configure() {
 	# See bug #676468 (may be able to drop this if we adapt fix-32bit-BE.patch)?
 	mv prebuilt/32-bit-big-endian{,.broken} || die
 
+	# bug #944029
+	append-cflags -std=gnu17
+
 	local -a myconf=(
 		--program-suffix="-${SLOT}"
 		--infodir="${GUILE_INFODIR}"