Merging r369093:

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r369093 | lewis-revill | 2019-08-16 12:23:56 +0200 (Fri, 16 Aug 2019) | 11 lines

[RISCV] Add inline asm constraint A for RISC-V

This allows the constraint A to be used in inline asm for RISC-V, which
allows an address held in a register to be used.

This patch adds the minimal amount of code required to get operands with
the right constraints to compile.

Differential Revision: https://reviews.llvm.org/D54295


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llvm-svn: 369649