llvm: [ARM] Complete enumeration values for Tag_ABI_VFP_args

The LLD implementation of Tag_ABI_VFP_args needs to check the rarely
seen values of 3 (toolchain specific) and 4 compatible with both Base
and VFP.  Add the missing enumeration values so that LLD can refer to
them without having to use the raw numbers.

Obtained from:	llvm r338373 by Peter Smith

contrib/llvm/include/llvm/Support/ARMBuildAttributes.h

@@ -213,6 +213,8 @@ enum {
   // Tag_ABI_VFP_args, (=28), uleb128
   BaseAAPCS = 0,
   HardFPAAPCS = 1,
+  ToolChainFPPCS = 2,
+  CompatibleFPAAPCS = 3,
 
   // Tag_FP_HP_extension, (=36), uleb128
   AllowHPFP = 1, // Allow use of Half Precision FP