Remove use of AM_PROG_CC_STDC as AC_PROG_CC does it. And move to AC_CONFIG_HEADERS.
Remove use of AM_PROG_CC_STDC as AC_PROG_CC does it. And move to AC_CONFIG_HEADERS.

This commit is a port of two commits from E: r82135 and r82148.

zmike/echievements,zmike/echievements