When MySQL converted from autotools to CMake, the
preprocessor symbol USE_SYMDIR was omitted by mistake.
Without this symbol, the code for checking .sym files
is not built.
This patch defines USE_SYMDIR when built on MS Windows.
Bug : -DBUILD_CONFIG=mysql_release sets SIGNCODE parameter which requires
singtool.exe (part of Windows SDK) in order to be able to sign the binaries (
only if valid certificate is found). However singtool is not a part of the SDK shipped
with Visual Studio Express, so the build fails claiming missing singtools.exe
Fix: Do not use SIGNCODE wiith VC Express.
Also, fix broken nmake build (*.rc files could not be compiled due to ADD_DEFINITIONS
contaning C/C++ compiler specific flags)
