* Makefile.in (libexecdir): New.
(libsubdir): Use gcc instead of gcc-lib.
(libexecsubdir): New.
(ORDINARY_FLAGS_TO_PASS): Add libexecsubdir.
(DRIVER_DEFINES): Add STANDARD_LIBEXEC_PREFIX, use gcc instead of
gcc-lib.
(installdirs): Make libexecsubdir.
(install-common): Put executables in libexecsubdir.
(itoolsdir): Use libexecsubdir.
(itoolsdatadir): New.
(install-mkheaders): Separate data files and executables.
(install-collect2): Put executables in libexecsubdir.
(uninstall): Remove libexecsubdir.
* mkheaders.in: Update for new arrangement of files.
(libexecdir): New.
(libexecsubdir): New.
(itoolsdir): Use libexecsubdir.
(itoolsdatadir): New.
* gcc.c (gcc_libexec_prefix): New.
(STANDARD_LIBEXEC_PREFIX): Use gcc instead of gcc-lib.
(standard_exec_prefix_1): Use libexec.
(standard_exec_prefix_2): New.
(standard_libexec_prefix): New.
(process_command): Update for new arrangement of files. Compute
gcc_libexec_prefix. Update for change from gcc-lib to gcc.