Mention the relevant GCC bug ID

Change-Id: I3edd39ce3180383c5274380896a0b3884bd08998
diff --git a/configure.ac b/configure.ac
index 5a80887..50b75fa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6336,6 +6336,9 @@ then
fi
AC_LANG_PUSH([C++])
AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
    // A somewhat over-complicated way of checking for
    // <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66460> "ICE using __func__
    // in constexpr function":
    #include <cassert>
    template<typename T> inline constexpr T f(T x) { return x; }
    template<typename T> inline constexpr T g(T x) {