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

[thakis]

Summary

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).

[hans]

lgtm

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

 }
 
 declare_args() {
   # Set if the host compiler is clang.  On by default on Mac or if
   # clang_base_path is set.
   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 != ""
 }