Microsoft C++ compiler is a Windows-based compiler used to compile Symbian OS code for the emulator. See GCC, GCCE or RVCT for compilation for the target.
Microsoft C++ compiler is used in the old Symbian OS SDKs to compile against WINS target platform. The newer Symbian OS SDKs do not require Microsoft C++ compiler any longer. They use x86 compiler to compile for the emulator. The target platform for x86 compiler is called WINSCW.