[CMake] Add detection for the mold linker in AddLLVM.cmake.

[fcambus]

Summary

mold says it is compatible with GNU ld and gold linkers:

$ mold -v
mold 0.9.5 (compatible with GNU ld and GNU gold)

And thus it currently gets detected as Gold.

With the following diff, CMake now correctly reports the linker name, and mold keeps being identified as Gold internally for now.

[ldionne]

and mold keeps being identified as Gold internally for now.

Why do we want to keep identifying it as Gold? I guess it's because additional work needs to happen if we don't just treat it as Gold?

LGTM.

[MaskRay]

llvm/cmake/modules/AddLLVM.cmake

198

LLVM_LINKER_IS_GOLD should be dropped

[fcambus]

Why do we want to keep identifying it as Gold? I guess it's because additional work needs to happen if we don't just treat it as Gold?

Wrong assumption on my part, there is in fact no need to keep identifying as Gold. Will send an updated revision.

[fcambus]

This revision drops the unneeded line setting LLVM_LINKER_IS_GOLD.

[fcambus]

@MaskRay I don't have commit access, could you commit this for me? Thanks!

[xgupta]

done.

llvm/cmake/modules/AddLLVM.cmake

else()
       separate_arguments(flags UNIX_COMMAND "${CMAKE_EXE_LINKER_FLAGS}")
       set(command ${CMAKE_C_COMPILER} ${flags} -Wl,--version)
     endif()
     execute_process(
       COMMAND ${command}
       OUTPUT_VARIABLE stdout
       ERROR_VARIABLE stderr
       )
-    if("${stdout}" MATCHES "GNU gold")
+    if("${stdout}" MATCHES "^mold")
+      set(LLVM_LINKER_DETECTED YES CACHE INTERNAL "")
+      set(LLVM_LINKER_IS_GOLD YES CACHE INTERNAL "")
+      message(STATUS "Linker detection: mold")
+    elseif("${stdout}" MATCHES "GNU gold")
       set(LLVM_LINKER_DETECTED YES CACHE INTERNAL "")
       set(LLVM_LINKER_IS_GOLD YES CACHE INTERNAL "")
       message(STATUS "Linker detection: GNU Gold")
     elseif("${stdout}" MATCHES "^LLD")
       set(LLVM_LINKER_DETECTED YES CACHE INTERNAL "")
       set(LLVM_LINKER_IS_LLD YES CACHE INTERNAL "")
       message(STATUS "Linker detection: LLD")
     elseif("${stdout}" MATCHES "GNU ld")