Revise unittest for 'LD' in 'make_global_settings'

This is a follow up CL for r1937. This is just a revise of a unittest and does not changes existing functionality.

It turned out that we need to specify GYP_CROSSCOMPILE=1 to test 'LD'/'LD.host' properly. Expected results, which are expected to be describing the current behavior, are updated accordingly.

BUG=gyp:434
TEST=unittest
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/338523003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1939 78cadc50-ecff-11dd-a971-7dbc132099af