gn: bootstrap: always use cxx for linking

LD may be set to something like "ld.bfd" or "ld.gold". We want to let
the compiler invoke the linker instead of calling these directly.

Bug: https://bugs.gentoo.org/597218
Review-Url: https://codereview.chromium.org/2422203002
Cr-Original-Commit-Position: refs/heads/master@{#425723}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 11aa518d0b8d280fdc5958ae440a4f799fa6ac56

tools/gn/bootstrap/bootstrap.py

diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index b86757a..d66da12 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -288,7 +288,7 @@
   else:
     cc = os.environ.get('CC', 'cc')
     cxx = os.environ.get('CXX', 'c++')
-    ld = os.environ.get('LD', cxx)
+    ld = cxx
     ar = os.environ.get('AR', 'ar')
 
   cflags = os.environ.get('CFLAGS', '').split()