Tests: Move LINK_SEARCH_{START,END}_STATIC case to dedicated test

The test case added to RunCMake.set_property by commit 675ef165 (Allow
LINK_SEARCH_{START,END}_STATIC props to have default values, 2015-08-07)
is not a test of the set_property command and so belongs in its own test
case.  Create a new RunCMake.LinkStatic test to cover cases related to
static linking.

While at it, simplify the LINK_SEARCH_STATIC test case to enable only C.