fbreader: fix gcc6 build

No revbump because gcc4 is not affected.

srcpkgs/fbreader/template

@@ -12,6 +12,12 @@ homepage="http://www.fbreader.org/"
 distfiles="http://www.fbreader.org/files/desktop/${pkgname}-sources-${version}.tgz"
 checksum=3d7c31d5ea314589d2a963290ad16f4d3d631a41e802b8b39f8be0c9f71eb8e9
 
+_gccver=$(gcc --version | awk '/^gcc \(GCC\)/ { print $3 }')
+if [ "${_gccver%%.*}" -gt 5 ]; then
+	CFLAGS="-Wno-error=narrowing"
+	CXXFLAGS="-Wno-error=narrowing"
+fi
+
 post_configure() {
 	sed -i makefiles/arch/desktop.mk \
 		-e"s;^\(CFLAGS.*=.*\);& $CFLAGS;" \