Use a GN arg for controlling linker map file generation.

build/toolchain/gcc_toolchain.gni

Index: build/toolchain/gcc_toolchain.gni
diff --git a/build/toolchain/gcc_toolchain.gni b/build/toolchain/gcc_toolchain.gni
index fa0de63052aeae948fca9aa10f020d63db87bd9b..d7286635a3d61e50b01f805e54d515422dd2df98 100644
--- a/build/toolchain/gcc_toolchain.gni
+++ b/build/toolchain/gcc_toolchain.gni
@@ -254,10 +254,8 @@ template("gcc_toolchain") {
       extra_ldflags = ""
     }
 
-    # Currently disabled on LLD because of a bug (fixed upstream).

[agrieve, 2017/05/17 14:33:11]

nit: can you preserve this comment by moving it to the declare_args() for
enable_linker_map

[estevenson, 2017/05/17 23:02:08]

Done.

-    # See https://crbug.com/716209.
     enable_linker_map = defined(invoker.enable_linker_map) &&
-                        invoker.enable_linker_map && !use_lld
+                        invoker.enable_linker_map && generate_linker_map
 
     # These library switches can apply to all tools below.
     lib_switch = "-l"