audk/BaseTools/building-gcc.txt

To use GCC with the BaseTools project for edk2 based development purposes,
you will need to build a GCC based cross-compiler (in addition to binutils).

Instructions for building GCC for this purpose can be found under the
BaseTools source tree.  (In addition to the instructions, you will also
find scripts to help automate the build process.)

If you do not have a tianocore.org account, you can make use of the 'guest'
account with an empty password.

In a web browser, you can 'browse' the relavent source at this location:
 http://sourceforge.net/p/edk2-buildtools/code/HEAD/tree/trunk/BaseTools/gcc

Or, with subversion, you can download the relavent source with this command:
 svn co https://svn.code.sf.net/p/edk2-buildtools/code/trunk/BaseTools/gcc