libtool: check Sun Pro CXX ABI postdeps at libtool time.

* m4/libtool.m4 (_LT_PREPARE_CC_BASENAME): Factor cc_basename
calculation into a shell function...
(_LT_CONFIG_SAVE_COMMAND): ...and expand it into generated
libtool script.
(_LT_CC_BASENAME): Adjust accordingly.
(_LT_FUNC_SUNCC_CSTD_ABI): Remove from here...
* build-aux/ltmain.in (func_suncc_cstd_abi): ...and reimplement
here.
* m4/libtool.m4 (_LT_SYS_HIDDEN_LIBDEPS): Remove postdeps
augmentation from here...
* build-aux/ltmain.in (func_mode_link): ...and reimplement here
just before postdeps are added.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>