configure.ac: rework wayland-protocols handling

At dist/distcheck time we need to ensure that all the files and their
respective dependencies are handled.

At the moment we'll bail out as the linux-dmabuf rules are guarded in a
conditional. Move them outside of it and drop the sources from
BUILT_SOURCES.

Thus the files will be generated only as needed, which will happen only
after the wayland-protocols dependency is enforced in configure.ac.

v2: add dependency tracking for the header

Cc: Andres Gomez <agomez@igalia.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Andres Gomez <agomez@igalia.com>
diff --git a/configure.ac b/configure.ac
index 2689fc5..2736fbf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1681,19 +1681,26 @@
     AC_PATH_PROG([WAYLAND_SCANNER], [wayland-scanner], [:])
 fi
 
+PKG_CHECK_EXISTS([wayland-protocols >= $WAYLAND_PROTOCOLS_REQUIRED], [have_wayland_protocols=yes], [have_wayland_protocols=no])
+if test "x$have_wayland_protocols" = xyes; then
+    ac_wayland_protocols_pkgdatadir=`$PKG_CONFIG --variable=pkgdatadir wayland-protocols`
+fi
+AC_SUBST(WAYLAND_PROTOCOLS_DATADIR, $ac_wayland_protocols_pkgdatadir)
+
 # Do per platform setups and checks
 platforms=`IFS=', '; echo $with_platforms`
 for plat in $platforms; do
     case "$plat" in
     wayland)
 
-        PKG_CHECK_MODULES([WAYLAND], [wayland-client >= $WAYLAND_REQUIRED wayland-server >= $WAYLAND_REQUIRED wayland-protocols >= $WAYLAND_PROTOCOLS_REQUIRED])
-        ac_wayland_protocols_pkgdatadir=`$PKG_CONFIG --variable=pkgdatadir wayland-protocols`
-        AC_SUBST(WAYLAND_PROTOCOLS_DATADIR, $ac_wayland_protocols_pkgdatadir)
+        PKG_CHECK_MODULES([WAYLAND], [wayland-client >= $WAYLAND_REQUIRED wayland-server >= $WAYLAND_REQUIRED])
 
         if test "x$WAYLAND_SCANNER" = "x:"; then
                 AC_MSG_ERROR([wayland-scanner is needed to compile the wayland platform])
         fi
+        if test "x$have_wayland_protocols" = xno; then
+                AC_MSG_ERROR([wayland-protocols >= $WAYLAND_PROTOCOLS_REQUIRED is needed to compile the wayland platform])
+        fi
         DEFINES="$DEFINES -DHAVE_WAYLAND_PLATFORM"
         ;;