Support AC_REQUIRE_AUX_FILE, and fix requirement of AM_PROG_CC_C_O.

Support AC_REQUIRE_AUX_FILE, and fix requirement of AM_PROG_CC_C_O.
* automake.in (%required_aux_file): New hash.
(handle_single_transform, lang_c_rewrite): Do note explicitly
require 'compile', this is now an internal detail of
AM_PROG_CC_C_O.
(scan_autoconf_traces): Trace AC_REQUIRE_AUX_FILE and fill
%required_aux_file.
(scan_autoconf_files): Require all %required_aux_file instead
of explicitly requiring install-sh and missing.
(generate_makefile): Do not require config.sub and config.guess.
(handle_single_transform): Pass $have_per_exec_flags to
&lang_c_rewrite.
* configure.ac, m4/init.m4: Require Autoconf 2.59a.
* doc/automake.texi (Optional): Document AC_REQUIRE_AUX_FILE.
(Program and Library Variables, Options, Public macros):
AC_PROG_CC_C_O is required when per-target flags or subdir-objects
are used with C sources.
* m4/minuso.m4: Require `compile' using AC_REQUIRE_AUX_FILE.
* m4/missing.m4: Require `missing' similarly.
* tests/acsubst2.test, tests/distcom2.test, tests/distcom6.test,
tests/specflg.test, tests/specflg2.test, tests/specflg3.test,
tests/specflg6.test, tests/specflg7.test, tests/specflg8.test,
tests/specflg9.test, tests/subobj7.test, tests/target-cflags.test,
tests/yacc6.test: Fix to use AM_PROG_CC_C_O.