enabled versioned MinGW-w64 .dlls on cmake

[Adsun701]

This enables versioned .dll shared libraries on cmake using MinGW-w64, in concurrence with autotools also producing versioned .dll shared libraries.

[willson-chen]

I performed the following steps in Win10 with cmake and MinGW:

mkdir build
cd build
cmake -G"Unix Makefiles" ..
make

But I can't find any dll file. Did I do it wrong? @Adsun701

[Adsun701]

@willson-chen The generator should be MSYS Makefiles.

EDIT: If you are using a Windows command prompt, the appropriate generator should be MinGW Makefiles. If you are using MSYS2 shell, use MSYS Makefiles. If you are cross-compiling from Linux, then use Unix Makefiles.

[willson-chen]

Sorry...It failed again. I had tried MSYS2 with cmake -G "MSYS Makefiles" .., but still no dll was found.
And referencing #63 , I am not sure building dynamic and static libs at the same time is nessary.