BaseTools: Implement BUILDRULEORDER for tools_def

BaseTools: Implement BUILDRULEORDER for tools_def

This feature allows the toolchain to choose a preference for source file
extensions in tools_def.txt. The first extension is given the highest priority.

Here is an example usage for tools_def.txt:
*_*_*_*_BUILDRULEORDER         = nasm Nasm NASM asm Asm ASM S s
*_XCODE5_*_*_BUILDRULEORDER    = S s nasm Nasm NASM

Now, if a .inf lists these sources: 1.nasm, 1.asm and 1.S
All toolchains, except XCODE5 will use the 1.nasm file. The XCODE5
toolchain will use the 1.S file.

Note that the build_rule.txt file also impacts the decision, because,
for instance there is no build rule for .asm files on GCC toolchains.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yingke Liu <yingke.d.liu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17509 6f19259b-4bc3-4df7-8a09-765794883524