Pass the gold binary to the linker using only absolute paths.

The previous expansion using <(PRODUCT_DIR)/../.. did not work correctly
if one was using a different build directory layout (out-of-source
builds, or some build directory with a different number of
subdirectories).

Solve this by doing the same as the sysroot variables: stop using
relative paths from the build directory and extract absolute paths using
DEPTH.

TEST=./build/gyp_chromium -Goutput_dir=/somewhere/else
R=phajdan.jr@chromium.org,thakis@chromium.org,dpranke@chromium.org

Review URL: https://codereview.chromium.org/83673002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236822 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236822