[gn build] Use LLD as host linker by default on macOS if clang_base_path is set

lld/mac should be stable enough to use it as host linker. I've been
using `use_lld=true` in my local args.gn for many months now and it
works fine (and links much faster than ld64).

Differential Revision: https://reviews.llvm.org/D112622

llvm/utils/gn/build/toolchain/compiler.gni

@@ -21,5 +21,5 @@ declare_args() {
   is_clang = host_os == "mac" || clang_base_path != ""
 
   # Set this to true to link with LLD instead of the default linker.
-  use_lld = clang_base_path != "" && host_os != "mac"
+  use_lld = clang_base_path != ""
 }