EmulatorPkg: Enable CLANG9 tool chain

EmulatorPkg: Enable CLANG9 tool chain

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1603
1. Add WIN_HOST_BUILD macro check for CLANG9 tool chain
build -p EmulatorPkg\EmulatorPkg.dsc -a IA32 -DWIN_HOST_BUILD=TRUE -t CLANG9
build -p EmulatorPkg\EmulatorPkg.dsc -a X64 -DWIN_HOST_BUILD=TRUE -t CLANG9
2. Append CLANG CC and LINK flags to generate windows HOST.
3. Fix WinHost issue to call GetProcessAffinityMask() API.
   The input parameter should be UINTN pointer instead of UINT32 pointer.

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Andrew Fish <afish@apple.com>
Cc: Ray Ni <ray.ni@intel.com>
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>