app-accessibility/espeak: fix build w/ clang 16

Closes: https://bugs.gentoo.org/894180
Signed-off-by: Sam James <sam@gentoo.org>

app-accessibility/espeak/espeak-1.48.04-r1.ebuild

@@ -1,9 +1,9 @@
-# Copyright 1999-2022 Gentoo Authors
+# Copyright 1999-2023 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 EAPI=6
 
-inherit toolchain-funcs
+inherit flag-o-matic toolchain-funcs
 
 MY_P="${P}-source"
 SRC_URI="mirror://sourceforge/${PN}/${MY_P}.zip"
@@ -46,6 +46,9 @@ src_prepare() {
 }
 
 src_compile() {
+	# Uses removed 'register' keyword, bug #894180
+	append-flags -std=c++14
+
 	emake \
 		PREFIX="${EPREFIX}/usr" \
 		CC="$(tc-getCC)" \