configure.ac: drop AM_PROG_CC_C_O invocation
configure.ac: drop AM_PROG_CC_C_O invocation

It's unnecessary since Automake 1.14.

Signed-off-by: Benjamin Gilbert <55d1d0083477f6dd5757d8929dd3b9e09d80bd84@cs.cmu.edu>

openslide/openslide,openslide/openslide,openslide/openslide,openslide/openslide