[CMake] Win32 Executable.

[Surya Kiran Gullapalli]

Hi all,
I'm building a win32 application, and for that I wanted to build the
application as console application in debug mode and win32 application
in release mode.

ADD_EXECUTABLE takes care of /subsystem:windows or /subsystem:console
flag, depends on whether or not you provide WIN32 flag to
ADD_EXECUTABLE.

I switch between debug and release builds quite often. It is very
inconvenient to modify the add_executable call every now and then. Is
there any way i can specify the appropriate flags at once (like we do
for
TARGET_LINK_LIBRARIES with debug and optimized flags).?

Surya