Limit number of concurrent links on Win x64 builder to 4.
Limit number of concurrent links on Win x64 builder to 4.

R=jschuh@chromium.org, scottmg@chromium.org
BUG=

Review URL: https://chromiumcodereview.appspot.com/23672042

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@223745 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build