[CMake][runtimes] Pass the CMAKE_ARGS to runtimes build correctly

[phosek]

Summary

We were relying on CMAKE_ARGS argument to be passed to subbuild, but
this argument was never properly defined. This patch addresses that.

[smeenai]

Hah, whoops. LGTM.

llvm/runtimes/CMakeLists.txt

llvm_ExternalProject_Add(runtimes
                                            ${SUB_INSTALL_TARGETS}
                              USE_TOOLCHAIN
                              ${EXTRA_ARGS})
   endfunction()
 
   # runtime_register_target(target)
   #   Utility function to register external runtime target.
   function(runtime_register_target name target)
-    cmake_parse_arguments(ARG "" "" "DEPENDS" ${ARGN})
+    cmake_parse_arguments(ARG "" "" "DEPENDS;CMAKE_ARGS" ${ARGN})
     include(${LLVM_BINARY_DIR}/runtimes/${name}/Components.cmake OPTIONAL)
     set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS ${LLVM_BINARY_DIR}/runtimes/${name}/Components.cmake)
 
     set(${name}_deps ${ARG_DEPENDS})
     if(NOT name STREQUAL target)
       list(APPEND ${name}_deps runtimes-${target})
     endif()
 
if(LLVM_INCLUDE_TESTS)
       foreach(target_name IN LISTS SUB_CHECK_TARGETS)
         set(${target_name}-${name} ${target_name})
         list(APPEND ${name}_test_targets ${target_name}-${name})
         list(APPEND test_targets ${target_name}-${name})
       endforeach()
       set(test_targets "${test_targets}" PARENT_SCOPE)
     endif()
 
+    set(${name}_extra_args ${ARG_CMAKE_ARGS})
     get_cmake_property(variableNames VARIABLES)
     foreach(variableName ${variableNames})
       string(FIND "${variableName}" "RUNTIMES_${target}_" out)
       if("${out}" EQUAL 0)
         string(REPLACE "RUNTIMES_${target}_" "" new_name ${variableName})
         string(REPLACE ";" "|" new_value "${${variableName}}")
         list(APPEND ${name}_extra_args "-D${new_name}=${new_value}")
       endif()