StdLib: Patches and updates for ARM.

Add ARMGCC and RVCT toolchain support.
Update and Add ARM specific machine headers.
Set the empty macro for __warn_references().
Make __flt_rounds() return 'Round to nearest' by default on ARM.

Signed-off-by:  Olivier Martin [olivier.martin@arm.com]
Reviewed-by:    darylm503


git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@12367 6f19259b-4bc3-4df7-8a09-765794883524
diff --git a/StdLib/StdLib.dsc b/StdLib/StdLib.dsc
index 717e2d8..c352b22 100644
--- a/StdLib/StdLib.dsc
+++ b/StdLib/StdLib.dsc
@@ -25,7 +25,7 @@
   PLATFORM_VERSION               = 0.01

   DSC_SPECIFICATION              = 0x00010006

   OUTPUT_DIRECTORY               = Build/StdLib

-  SUPPORTED_ARCHITECTURES        = IA32|IPF|X64

+  SUPPORTED_ARCHITECTURES        = IA32|IPF|X64|ARM

   BUILD_TARGETS                  = DEBUG|RELEASE

   SKUID_IDENTIFIER               = DEFAULT