wayland-egl: fail the symbol check if lib is missing

Based on a similar patch (in Mesa) by Eric Engestrom.

v2: Rebase on top of $NM patch
v3: Rebase

Reviewed-by: Eric Engestrom <eric@engestrom.ch> (v1)
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>

egl/wayland-egl-symbols-check

 #!/bin/sh
+set -eu
 
-FUNCS=$($NM -D --defined-only ${WAYLAND_EGL_LIB} | grep -o "T .*" | cut -c 3- | while read func; do
+LIB=${WAYLAND_EGL_LIB}
+
+if [ ! -f "$LIB" ]; then
+	echo "The test binary \"$LIB\" does no exist"
+	exit 1
+fi
+
+FUNCS=$($NM -D --defined-only $LIB | grep -o "T .*" | cut -c 3- | while read func; do
 ( grep -q "^$func$" || echo $func )  <<EOF
 wl_egl_window_resize
 wl_egl_window_create