BaseTools: Modify gcc 4.8 and 4.9 tool chain definition to support building from Windows. 
    
    Here is a new patch that adds Windows support for both gcc 4.8.x and gcc 4.9.x. 
    This time testing is more thorough: boot testing using Duet for all 4 combinations of 
    IA32/X64 and gcc 4.8.2 and gcc 4.9.1 passes. A Windows hosted gcc 4.8.2 has been added here:
    http://sourceforge.net/projects/edk2developertoolsforwindows/
    
    The environment variable settings for Windows look like:
    
    set UEFI_BUILD_TOOLS=%cd%\tools
    set NASM_PREFIX=%UEFI_BUILD_TOOLS%\nasm211\
    set GCC48_BIN=%UEFI_BUILD_TOOLS%\gcc482-x86\bin\
    set GCC48_DLL=%UEFI_BUILD_TOOLS%\gcc482-x86\dll\;%GCC48_BIN%
    set GCC48_ARM_PREFIX=%UEFI_BUILD_TOOLS%\gcc482-arm\bin\
    set GCC48_AARCH64_PREFIX=%UEFI_BUILD_TOOLS%\gcc482-aarch64\bin\
    set GCC49_BIN=%UEFI_BUILD_TOOLS%\gcc491-x86\bin\
    set GCC49_DLL=%UEFI_BUILD_TOOLS%\gcc491-x86\dll\;%GCC49_BIN%
    set GCC49_ARM_PREFIX=%UEFI_BUILD_TOOLS%\gcc491-arm\bin\
    set GCC49_AARCH64_PREFIX=%UEFI_BUILD_TOOLS%\gcc491-aarch64\bin\
    
    No change is needed for building from Linux. 
    
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Scott Duplichan <scott@notabs.org>
    Reviewed-by: Liming Gao <liming.gao@intel.com>
    
    git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16400 6f19259b-4bc3-4df7-8a09-765794883524