[libclc] [libclc] Skip opt command if opt_flags is empty (PR #130882)

[Fraser Cormack via cfe-commits]

================
@@ -342,22 +342,32 @@ function(add_libclc_builtin_set)
 
   set( builtins_opt_lib_tgt builtins.opt.${ARG_ARCH_SUFFIX} )
 
-  # Add opt target
-  add_custom_command( OUTPUT ${builtins_opt_lib_tgt}.bc
-    COMMAND ${opt_exe} ${ARG_OPT_FLAGS} -o ${builtins_opt_lib_tgt}.bc
-      ${builtins_link_lib}
-    DEPENDS ${opt_target} ${builtins_link_lib} ${builtins_link_lib_tgt}
-  )
-  add_custom_target( ${builtins_opt_lib_tgt}
-    ALL DEPENDS ${builtins_opt_lib_tgt}.bc
-  )
+  if( ${ARG_OPT_FLAGS} STREQUAL "" )
----------------
frasercrmck wrote:

I just realised this code isn't triggered upstream. I take it you have a downstream making use of it?

I tried it locally and this needs to be `if( "${ARG_OPT_FLAGS} STREQUAL "" )` or maybe better yet `if ( NOT ARG_OPT_FLAGS )`. The code as-is generates an error if I pass in an empty OPT_FLAGS:

```
CMake Error at /llvm-project/libclc/cmake/modules/AddLibclc.cmake:345 (if):
  if given arguments:

    "STREQUAL" ""

  Unknown arguments specified
```

https://github.com/llvm/llvm-project/pull/130882