fix configure check for gcc
This shouldn't fail just because someone sets CC=gcc-4.5
explicitly. Besides, this way it also works with compilers
that advertise GCC-compatibility like clang and ICC.
diff --git a/configure.ac b/configure.ac
index 226d87c..a4cfcbf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -64,7 +64,7 @@
AS_IF([test "x$have_cairo_egl" = "xyes"],
[AC_DEFINE([HAVE_CAIRO_EGL], [1], [Have cairo-egl])])
-if test $CC = gcc; then
+if test "x$GCC" = "xyes"; then
GCC_CFLAGS="-Wall -g -Wstrict-prototypes -Wmissing-prototypes -fvisibility=hidden"
fi
AC_SUBST(GCC_CFLAGS)