Patch merged into coreboot/master: buildgcc: Add option to bootstrap a host gcc

the following patch was just integrated into master:
commit 234d246535029e92209ed0371b6cae6506807d0a
Author: Nico Huber 
Date:   Tue Jan 26 16:10:17 2016 +0100

buildgcc: Add option to bootstrap a host gcc

Bootstrapping gcc is the recommended way if your host gcc's version
    doesn't match the gcc version you're going to build. While a build
    with an outdated host gcc usually succeeds, an outdated gnat seems
    to be a bigger issue.

v3: Some library controversy: gcc likes the libraries it ships with
        most but we don't want to install shared libraries. So we build
        them static --disable-shared) and install only the minimum
        (libgcc, libada, libstdc++). However, as the code of these
        libraries might be used to build a shared library we have to
        compile them with `-fPIC`.

v4: o Updated getopt strings.
        o The workaround for clang (-fbracket-depth=1024) isn't needed
          for bootstrapping and also breaks the build, as clang is only
          used for the first stage in that case and gcc doesn't know
          that option.

So far build tested with `make BUILDGCC_OPTIONS="-b -l c,ada"` on
      o Ubuntu 14.04 "Trusty Tahr" (i386)
      o Debian 8 "Jessie" (x86_64) (building python (-S) works too)
      o current Arch Linux (x86_64)
      o FreeBSD 10.3 (x86_64) (with gcc-aux package)

and with clang host compiler, thus C only: `make BUILDGCC_OPTIONS="-b"`
    on
      o Debian 8 "Jessie" (x86_64)
      o FreeBSD 10.3 (x86_64)

v5: Rebased after toolchain updates to GCC 5.3.0 etc.

Build tested with `make BUILDGCC_OPTIONS="-b -l c,ada"` on
      o Debian 8 "Jessie" (x86_64)

Change-Id: Icb47d3e9dbafc55737fbc3ce62a084fb9d5f359a
    Signed-off-by: Nico Huber 
    Reviewed-on: https://review.coreboot.org/13473
    Tested-by: build bot (Jenkins)
    Reviewed-by: Patrick Georgi

See https://review.coreboot.org/13473 for details.

-gerrit