Hook up OpenBSD 64-bit RISC-V support

(cherry picked from commit 592b899)

Author: brad0

clang/lib/Basic/Targets.cpp

@@ -391,6 +391,8 @@ TargetInfo *AllocateTarget(const llvm::Triple &Triple,
     switch (os) {
     case llvm::Triple::FreeBSD:
       return new FreeBSDTargetInfo<RISCV64TargetInfo>(Triple, Opts);
+    case llvm::Triple::OpenBSD:
+      return new OpenBSDTargetInfo<RISCV64TargetInfo>(Triple, Opts);
     case llvm::Triple::Fuchsia:
       return new FuchsiaTargetInfo<RISCV64TargetInfo>(Triple, Opts);
     case llvm::Triple::Linux:

clang/test/Preprocessor/init.c

@@ -7326,6 +7326,7 @@
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=mips64-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=mips64el-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
 // RUN: %clang_cc1 -E -dM -ffreestanding -triple=sparc64-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
+// RUN: %clang_cc1 -E -dM -ffreestanding -triple=riscv64-unknown-openbsd6.1 < /dev/null | FileCheck -match-full-lines -check-prefix OPENBSD %s
 // OPENBSD:#define __ELF__ 1
 // OPENBSD:#define __INT16_TYPE__ short
 // OPENBSD:#define __INT32_TYPE__ int