Disable linker map for Clang toolchains.

Right now, we are transitioning to LLD, and LLD has a different
map format (so, the analysis tool will need to be updated), as well as
suboptimal implementation that adds 60 minutes to the Chrome link time.

This will be reenabled when both of the blockers above are resolved.

BUG=716209,607968

Review-Url: https://codereview.chromium.org/2849583005
Cr-Commit-Position: refs/heads/master@{#468113}

build/toolchain/gcc_toolchain.gni

@@ -248,8 +248,10 @@ template("gcc_toolchain") {
       extra_ldflags = ""
     }
 
-    enable_linker_map =
-        defined(invoker.enable_linker_map) && invoker.enable_linker_map
+    # Currently disabled on LLD because of a bug (fixed upstream).
+    # See https://crbug.com/716209.
+    enable_linker_map = defined(invoker.enable_linker_map) &&
+                        invoker.enable_linker_map && !use_lld
 
     # These library switches can apply to all tools below.
     lib_switch = "-l"