StdLib/LibC: Fix ARM symbol problems

StdLib/LibC: Fix ARM symbol problems
StdLibPrivateInternalFiles: Add AArch64 support

Disable 'memcpy' symbol for ARM in LibC. It is already provided by the ARM compiler intrinsics library.
Add missing 'strtold' symbol. Use the same fallback as IPF for now.
Use Include definitions as provided by ARM version.

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 <daryl.mcdaniel@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15858 6f19259b-4bc3-4df7-8a09-765794883524