[CMake][compiler-rt][RISCV] Support RISC-V cross-compilation

[luismarques]

Summary

This seems to be a safe way to ensure that the Compiler-RT test compiler flags are properly set in all cross-compilation scenarios. Without this when BUILTINS_TEST_TARGET_CFLAGS is set in compiler-rt/test/builtins/CMakeLists.txt the other flags are cleared (I had been using a different workaround for that issue).

@pzheng had suggested an alternative fix in [1]:

-  if(ANDROID OR ${arch} MATCHES "arm|aarch64")
+  if(ANDROID OR ${arch} MATCHES "arm|aarch64" OR
+      COMPILER_RT_TEST_COMPILER_CFLAGS)

I'm not sure that's correct and safe in all scenarios. If it is, couldn't the COMPILER_RT_TEST_COMPILER_CFLAGS condition subsume the other ones anyway? If the answer to this isn't clear I suggest we just add the RISC-V matches for now, as done in this patch.

[1] https://bugs.llvm.org/show_bug.cgi?id=44244

[luismarques]

Ping.

[lenary]

LGTM

compiler-rt/cmake/config-ix.cmake

else()
     endif()
   endif()
 endfunction()
 
 # Returns a compiler and CFLAGS that should be used to run tests for the
 # specific architecture.  When cross-compiling, this is controled via
 # COMPILER_RT_TEST_COMPILER and COMPILER_RT_TEST_COMPILER_CFLAGS.
 macro(get_test_cc_for_arch arch cc_out cflags_out)
-  if(ANDROID OR ${arch} MATCHES "arm|aarch64")
+  if(ANDROID OR ${arch} MATCHES "arm|aarch64|riscv32|riscv64")
     # This is only true if we are cross-compiling.
     # Build all tests with host compiler and use host tools.
     set(${cc_out} ${COMPILER_RT_TEST_COMPILER})
     set(${cflags_out} ${COMPILER_RT_TEST_COMPILER_CFLAGS})
   else()
     get_target_flags_for_arch(${arch} ${cflags_out})
     if(APPLE)
       list(APPEND ${cflags_out} ${DARWIN_osx_CFLAGS})