gcc_build: Add gcc bootstrap version scripts.
Update for the previous commit.
Update gcc_build

 - Update to upstream of gcc-4_9-branch.
 - Update 0011-gcc-use-build-sysroot-dir.patch:
     Raplace build_tooldir with build_sysroot.
 - Add 0013-LAA-default.patch
     Add --large-address-aware when building executables, not DLLs for 32 bit.
 - Specify -march/-mtune expressly. -march=sandybridge is buggy.
 - Symlink lto plugin into /mingw{32,64}/lib/bfd-plugins. This is needed for slim LTO.
buildscripts: Update for the previous commit.
gcc_build: delete non-bootstrap ver.
gcc_build: Improve symlink handling.