add a new gb_LinkTarget_use_system_win32_libs to abstract different
linker options on MSVC and GCC.
Change-Id: Ic9bf2545f59bf7871e6fc06b290c486ddfbec03d
Naming convention for gbuild methods:
- "add" is used for stuff that is logically a part of the target
(i.e. not registered at the Module, but defined in the target's makefile)
- "use" is used for stuff that is logically a different target
(i.e. it is registered at the Module, has it's own makefile, may be
in a different module than the target)
