Build system changes for RISCV

Summary: Build system changes for RISCV. Makes it possible to build just the RISCV target alone.

Reviewers: asb, apazos, mgrang, beanz

Reviewed By: asb

Subscribers: mgorny, kito-cheng, shiva0217, llvm-commits

Differential Revision: https://reviews.llvm.org/D44153

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327423 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/config-ix.cmake

@@ -441,6 +441,10 @@ elseif (LLVM_NATIVE_ARCH MATCHES "wasm32")
   set(LLVM_NATIVE_ARCH WebAssembly)
 elseif (LLVM_NATIVE_ARCH MATCHES "wasm64")
   set(LLVM_NATIVE_ARCH WebAssembly)
+elseif (LLVM_NATIVE_ARCH MATCHES "riscv32")
+  set(LLVM_NATIVE_ARCH RISCV)
+elseif (LLVM_NATIVE_ARCH MATCHES "riscv64")
+  set(LLVM_NATIVE_ARCH RISCV)
 else ()
   message(FATAL_ERROR "Unknown architecture ${LLVM_NATIVE_ARCH}")
 endif ()