* Allow skipping parts of the installation to be able to do it in parts if one

  phase fails and the user wants to reinstall one of the components.
* Fixed LLVM-GCC configuration flags: s/--with-gnu-{as,ld}/--with-{as,ld}/
  The former is a boolean flag, the latter is a flag that takes a path.
* Added a new flag CROSS_MARCH, defaults to armv6.

llvm-svn: 74840