This solves compilation issues from the future.
--- /dev/null
+diff -ru libtheora/configure.ac libtheora-fixed/configure.ac
+--- libtheora/configure.ac 2009-10-01 20:00:33.000000000 +0200
++++ libtheora-fixed/configure.ac 2014-06-13 20:21:16.000000000 +0200
+@@ -155,8 +155,20 @@
+
+ dnl Set some target options
+
++cc_compiler=unknown
++AC_COMPILE_IFELSE([AC_LANG_SOURCE([[#if ! __clang__
++ #error
++ #endif
++ ]])],
++ cc_compiler=clang,
++ [AC_COMPILE_IFELSE([AC_LANG_SOURCE([[#if ! __GNUC__
++ #error
++ #endif
++ ]])],
++ cc_compiler=gcc, [])])
++
+ cflags_save="$CFLAGS"
+-if test -z "$GCC"; then
++if test $cc_compiler != "gcc" ; then
+ case $host in
+ *)
+ DEBUG="-g -DDEBUG"
libtheora: libtheora-$(THEORA_VERSION).tar.xz .sum-theora
$(UNPACK)
+ $(APPLY) $(SRC)/theora/libtheora-compiler-differentiation.patch
$(UPDATE_AUTOCONFIG)
$(MOVE)