Allow specifying opt dependencies

If optimizations use more than one cpu feature, allow
specifying them so that '--disable-X' still works

https://code.google.com/p/webm/issues/detail?id=854

Change-Id: I3108ea37b397371a2be84dd5f2380b304db23f18
diff --git a/build/make/rtcd.pl b/build/make/rtcd.pl
index 5b0cefa..40bcb33 100755
--- a/build/make/rtcd.pl
+++ b/build/make/rtcd.pl
@@ -49,7 +49,7 @@
 
 my %config = ();
 while (<CONFIG_FILE>) {
-  next if !/^CONFIG_/;
+  next if !/^(?:CONFIG_|HAVE_)/;
   chomp;
   my @pair = split /=/;
   $config{$pair[0]} = $pair[1];