StdLib/LibC: Provide missing ARM symbols

StdLib/LibC: Provide missing ARM symbols

Provide missing functionality by using files from LLVM.

Changes made:
- Formatting changes (tabs to spaces, DOS line endings etc).
- Simplified 'int_endianness.h' to work for our case.
- Added LLVM licence to the individual files.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Harry Liebel <Harry.Liebel@arm.com>
Reviewed-by: Olivier Martin <Olivier.Martin@arm.com>
Reviewed-by: Daryl McDaniel <edk2-lists@mc2research.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18117 6f19259b-4bc3-4df7-8a09-765794883524