linux: migrate linker --threads flag out of gyp

(Retry of r121148 with ChromeOS excluded.)

This just copies the flags used within gyp.

BUG=gyp:250

Review URL: http://codereview.chromium.org/9360032

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@121257 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed