* configure.in: Simplify by removing CPP etc.

* configure.in: Simplify by removing CPP etc.

(CPP_TEST_OPTIONS, NON_GNU_CPP, cc_specified, SPECIFIED_CFLAGS)
(SPECIFED_CPP, CPP, NON_GNU_CC, AC_PROG_CPP): Remove; not needed.
In particular we no longer need to fiddle with CPP, since we don't
use CPP specially any more.
(gl_EARLY): Invoke this after adjusting CC, so that it uses the
adjusted compiler.
(AC_PROG_INSTALL, AC_PROG_MKDIR_P, AC_PROG_RANLIB): Comment out,
since gl_EARLY and/or Autoconf already does these.