Re-enable threads on ClangToTLinuxLLD.

I added -no-threads flag to LLD in 7b18ff885c40874f8e4a417ad03376161b19de0a,
but it turned out that the slowness of the bot is generally slow,
and it is unlikely that LLD's change is the cause of the problem.
This patch restore the original setting.

BUG=670397

Review-Url: https://codereview.chromium.org/2556503003
Cr-Original-Commit-Position: refs/heads/master@{#436517}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ffa1f105690aea99deecbdfff6eb40128604b73a

config/compiler/BUILD.gn

@@ -321,12 +321,6 @@ config("compiler") {
 
   if (is_posix && use_lld && !is_nacl) {
     ldflags += [ "-fuse-ld=lld" ]
-
-    # LLD as of 2016/12/02 seems to behave poorly with multi-threading.
-    # Disable threads on LLD trunk bots to see if they hurt build time.
-    if (llvm_force_head_revision) {
-      ldflags += [ "-Wl,-no-threads" ]
-    }
   } else if (use_gold) {
     ldflags += [ "-fuse-ld=gold" ]
     if (is_android) {