expect: Fix build with GCC 15

Stick to C17 standard as GCC 15 switches to C23

(From OE-Core rev: 4ae08da819d1bc5fee382651c3fe074e9be9d86e)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/expect/expect_5.45.4.bb

@@ -42,6 +42,8 @@ S = "${WORKDIR}/${BPN}${PV}"
 
 EXTRA_AUTORECONF += "--exclude=aclocal"
 
+CFLAGS += "-std=gnu17"
+
 do_install:append() {
     mv ${D}${libdir}/expect${PV}/libexpect*.so ${D}${libdir}/
     install -m 0755 ${S}/fixline1 ${D}${libdir}/expect${PV}/