Fix Cmake build for MinGW (#580)
Fix Cmake build for MinGW (#580)

Seems certain targets/hosts failed without these, as "_MSC_VER" is
undefined on MinGW, which caused the 'pragma comment(lib "libname")' to
fail.

Fixes #575
yhirose/cpp-httplib,yhirose/cpp-httplib,yhirose/cpp-httplib,yhirose/cpp-httplib