[AArch64] Add parsing of aarch64_vector_pcs attribute.

This patch adds parsing support for the 'aarch64_vector_pcs'
calling convention attribute to calls and function declarations.

More information describing the vector ABI and procedure call standard
can be found here:

  https://developer.arm.com/products/software-development-tools/\
                            hpc/arm-compiler-for-hpc/vector-function-abi

Reviewers: t.p.northover, rnk, rengolin, javed.absar, thegameg, SjoerdMeijer

Reviewed By: SjoerdMeijer

Differential Revision: https://reviews.llvm.org/D51477

llvm-svn: 342030
diff --git a/llvm/lib/AsmParser/LLParser.cpp b/llvm/lib/AsmParser/LLParser.cpp
index e2ee8d6..1fce430 100644
--- a/llvm/lib/AsmParser/LLParser.cpp
+++ b/llvm/lib/AsmParser/LLParser.cpp
@@ -1874,6 +1874,7 @@
 ///   ::= 'arm_apcscc'
 ///   ::= 'arm_aapcscc'
 ///   ::= 'arm_aapcs_vfpcc'
+///   ::= 'aarch64_vector_pcs'
 ///   ::= 'msp430_intrcc'
 ///   ::= 'avr_intrcc'
 ///   ::= 'avr_signalcc'
@@ -1917,6 +1918,7 @@
   case lltok::kw_arm_apcscc:     CC = CallingConv::ARM_APCS; break;
   case lltok::kw_arm_aapcscc:    CC = CallingConv::ARM_AAPCS; break;
   case lltok::kw_arm_aapcs_vfpcc:CC = CallingConv::ARM_AAPCS_VFP; break;
+  case lltok::kw_aarch64_vector_pcs:CC = CallingConv::AArch64_VectorCall; break;
   case lltok::kw_msp430_intrcc:  CC = CallingConv::MSP430_INTR; break;
   case lltok::kw_avr_intrcc:     CC = CallingConv::AVR_INTR; break;
   case lltok::kw_avr_signalcc:   CC = CallingConv::AVR_SIGNAL; break;