This is r250676 with clang on amd64.
checking if cc supports -errwarn=E_NO_EXPLICIT_TYPE_GIVEN -errwarn=E_NO_IMPLICIT_DECL_ALLOWED... eval: ${xorg_cv_cc_flag__errwarn_E_NO_EXPLICIT_TYPE_GIVEN ...}: Bad substitution
===> Script "configure" failed unexpectedly.
Do you need config.log?