MFC r247951:

Make c89(1) invoke /usr/bin/cc with argv[0] also set to /usr/bin/cc,
similar to what c99(1) does, to prevent "c89: illegal option -- 1"
messages, when clang is /usr/bin/cc.

Reported by:	tijl
MFC r247953:

Make c99(1) invoke /usr/bin/cc with argv[0] set to "/usr/bin/cc" instead
of just "cc", since there is no reason to cause additional path searches
in this case.