sdksyms: Tighten up the symbols we add to the magic table

The code as written would match anything declared extern. _X_EXPORT is
what we really mean here. That's a macro, so check for what it expands
to and skip if not found.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

hw/xfree86/sdksyms.sh

@@ -343,6 +343,10 @@ BEGIN {
            n = 1;
         }
 
+        # only match _X_EXPORT
+        if ($n !~ /^(__attribute__..visibility..default|__global)/)
+            next;
+
 	# skip attribute, if any
 	while ($n ~ /^(__attribute__|__global)/ ||
 	    # skip modifiers, if any