It was working fine for me, but someone had the error:
error: AC_PROG_CC cannot be called after AM_PROG_CC_C_O
/usr/share/aclocal/ax_prog_cc_for_build.m4:38: AX_PROG_CC_FOR_BUILD is expanded
from...
I can indeed see that AX_PROG_CC_FOR_BUILD code runs AC_PROG_CC again.
So let's make sure this is run before AM_PROG_CC_C_O.
Thanks to Francesco Riosa for reporting the bug.