Nt32Pkg SecMain: Update SecMain.inf to support VS2015x86 X64 Mode

Nt32Pkg SecMain: Update SecMain.inf to support VS2015x86 X64 Mode

In V2:
  Add the specific LIB path in IA32 LINK path.

Update SecMain.inf to support VS2015x86 X64 Mode Build.
After this change, X64 Native Tools Command Prompt is not
required to be trig. NT32 IA32 and X64 can be built in the same
environment. It simplifies NT32 X64 build. New build command:
edksetup.bat --nt32
build -p Nt32Pkg\Nt32Pkg.dsc -a X64  # for 64
build -p Nt32Pkg\Nt32Pkg.dsc -a IA32 # for 32

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: David Chan <chanuei@sina.com>
Tested-by: Liming Gao <liming.gao@intel.com>