[runtimes] When COMPILER_RT is enabled, consider SANITIZER prefixes

[phosek]

Summary

Currently we passthrough CMake variables based on project prefix,
i.e. LIBCXX_, LIBCXXABI_, LIBUNWIND_ and COMPILER_RT_. However, many
compiler-rt flags start with SANITIZER_ rather than COMPILER_RT, so
passthrough those as well.

[smeenai]

Good idea; this'll let us clean up some of our internal build setup as well. LGTM.

llvm/runtimes/CMakeLists.txt

else() # if this is included from LLVM's CMake
   # We create a list the names of all the runtime projects in all uppercase and
   # with dashes turned to underscores. This gives us the CMake variable prefixes
   # for all variables that will apply to runtimes.
   foreach(entry ${runtimes})
     get_filename_component(projName ${entry} NAME)
     string(REPLACE "-" "_" canon_name ${projName})
     string(TOUPPER ${canon_name} canon_name)
     list(APPEND prefixes ${canon_name})
+    # Many compiler-rt options start with SANITIZER_ rather than COMPILER_RT_,
+    # so when compiler-rt is enabled, consider both.
+    if(canon_name STREQUAL "COMPILER_RT")
+      list(APPEND prefixes SANITIZER)
+    endif()
 
     string(FIND ${projName} "lib" LIB_IDX)
     if(LIB_IDX EQUAL 0)
       string(SUBSTRING ${projName} 3 -1 projName)
     endif()
     list(APPEND runtime_names ${projName})
   endforeach()