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.
Use the CMAKE_LINK_SEARCH_START_STATIC and CMAKE_LINK_SEARCH_END_STATIC
variables to initialize the LINK_SEARCH_START_STATIC and
LINK_SEARCH_END_STATIC target properties respectively.
We use a special dedicated structure to store the LINK_LIBRARIES target
property. Do not try to construct a string from a NULL value. Instead
leave the property structure empty when no value is given.
Reported-by: Ghyslain Leclerc <ghleclerc@gmail.com>