Simplify the link specifications for libSG_java on win32 (untested).

The variable SIMGRID_LIB_NAME_NAME is never used, and probably gets an
undefined value here.  Remove its definition.

The variable SIMGRID_LIB_NAME is never set.  Remove reference to it.

Finally, use "target_link_libraries" for all platforms since I can't find any
reason to avoid it on win32.

Note that these changes are untested.