configure.ac: add AM_PROG_CC_C_O Older Automakes give this error without this directive: Makefile.am: C objects in subdir but `AM_PROG_CC_C_O' not in `configure.ac' In newer autotools this is included under AC_PROG_CC, but it's harmless to add. https://github.com/xkbcommon/libxkbcommon/issues/3 Signed-off-by: Ran Benita <ran234@gmail.com>