cmake: pass -static when STATIC=ON on Windows
cmake: pass -static when STATIC=ON on Windows

This gets rid of bitmonerod.exe's dependecy on libwindpthreads-1.dll in build
on Windows on x86_64 (via MSYS2 default toolchain). With this patch all DLL
dependencies are on DLLs in c:\windows\system32.

eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero,eiabea/bitmonero