GN: Build and link with LLD when using our Clang toolchain.

infra/bots/recipe_modules/flavor/gn_flavor.py

Index: infra/bots/recipe_modules/flavor/gn_flavor.py
diff --git a/infra/bots/recipe_modules/flavor/gn_flavor.py b/infra/bots/recipe_modules/flavor/gn_flavor.py
index f759d4bcc4edbabb7e6d52aed6c2ad701f0bfdb6..31b4756be0116842f08683d619c3ec9f3990491f 100644
--- a/infra/bots/recipe_modules/flavor/gn_flavor.py
+++ b/infra/bots/recipe_modules/flavor/gn_flavor.py
@@ -29,10 +29,12 @@ class GNFlavorUtils(default_flavor.DefaultFlavorUtils):
 
     cc, cxx = 'cc', 'c++'
     extra_cflags = []
+    extra_ldflags = []
 
     if compiler == 'Clang' and os == 'Ubuntu':
       cc  = self.m.vars.slave_dir.join('clang_linux', 'bin', 'clang')
       cxx = self.m.vars.slave_dir.join('clang_linux', 'bin', 'clang++')
+      extra_ldflags.append('-fuse-ld=lld')
     elif compiler == 'Clang':
       cc, cxx = 'clang', 'clang++'
     elif compiler == 'GCC':
@@ -57,6 +59,7 @@ class GNFlavorUtils(default_flavor.DefaultFlavorUtils):
         'cxx': quote(cxx),
         'compiler_prefix': quote(compiler_prefix),
         'extra_cflags': quote(' '.join(extra_cflags)),
+        'extra_ldflags': quote(' '.join(extra_ldflags)),
         'is_debug': 'true' if configuration == 'Debug' else 'false',
     }.iteritems()))