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"