Fix CMake config breakage in COMPILE_LANGUAGE generator

[etcwilde]

Summary

Listing multiple languages in the COMPILE_LANGUAGE generator is legal in CMake 3.15 and above, but not legal in earlier CMake versions.
Replacing that with an OR should behave the same way and be legal for older versions of CMake.

[compnerd]

Already committed in a43bf8078861ae816b45d94f7012a7ea01a2e5eb

[etcwilde]

Yep. Same change. Closing.

llvm/cmake/modules/HandleLLVMOptions.cmake

if( LLVM_ENABLE_ASSERTIONS )
   if( NOT MSVC )
     add_definitions( -D_DEBUG )
   endif()
   # On non-Debug builds cmake automatically defines NDEBUG, so we
   # explicitly undefine it:
   if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
     # NOTE: use `add_compile_options` rather than `add_definitions` since
     # `add_definitions` does not support generator expressions.
-    add_compile_options($<$<COMPILE_LANGUAGE:C,CXX>:-UNDEBUG>)
+    add_compile_options($<$<OR:$<COMPILE_LANGUAGE:C>,$<COMPILE_LANGUAGE:CXX>>:-UNDEBUG>)
 
     # Also remove /D NDEBUG to avoid MSVC warnings about conflicting defines.
     foreach (flags_var_to_scrub
         CMAKE_CXX_FLAGS_RELEASE
         CMAKE_CXX_FLAGS_RELWITHDEBINFO
         CMAKE_CXX_FLAGS_MINSIZEREL
         CMAKE_C_FLAGS_RELEASE
         CMAKE_C_FLAGS_RELWITHDEBINFO