[ARM] Complete enumeration values for Tag_ABI_VFP_args

[peter.smith]

Summary

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. We currently only have enum values for 0 (Base AAPCS) and 1 (VFP AAPCS), this patch adds the missing enumeration values so that LLD (D49993) can refer to them without having to use the raw numbers.

From Addenda to, and Errata in, the ABI for the Arm Architecture: http://infocenter.arm.com/help/topic/com.arm.doc.ihi0045e/IHI0045E_ABI_addenda.pdf

Tag_ABI_VFP_args, (=28), uleb128
0 The user intended FP parameter/result passing to conform to AAPCS, base variant
1 The user intended FP parameter/result passing to conform to AAPCS, VFP variant
2 The user intended FP parameter/result passing to conform to tool chain-specific
 conventions
3 Code is compatible with both the base and VFP variants; the user did not permit
 non-variadic functions to pass FP parameters/results

[grimar]

LGTM. Minor suggestion is bellow.

include/llvm/Support/ARMBuildAttributes.h

216

I am not sure, maybe Toolchain ->ToolChain since it is 2 different words in spec.

[peter.smith]

Thanks, I'll update the patches to use ToolChain on commit.

include/llvm/Support/ARMBuildAttributes.h

enum {
 
   // Tag_ABI_HardFP_use, (=27), uleb128
   HardFPImplied = 0,          // FP use should be implied by Tag_FP_arch
   HardFPSinglePrecision = 1,  // Single-precision only
 
   // 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
 
   // Tag_FP_16bit_format, (=38), uleb128
   FP16FormatIEEE = 1,
   FP16VFP3 = 2,