Fix mingw-w64 build

Add common_flags and common_ldflags to libgxps/meson.build, which are required in case of mingw-w64 builds.

• For mingw-w64 builds, COBJMACROS needs to be defined before any #include <jpeglib.h>, because jpeglib.h includes shlwapi.h, which provides a different IStream_Write and lacks IStream_Release.
  The correct include for IStream_Write and IStream_Release is objidl.h
  Fixes:

    gxps-images.c:1042:4: error: too many arguments to function 'IStream_Write'
    gxps-images.c:1058:2: error: implicit declaration of function 'IStream_Release'

• mingw-w64 builds require linking with libwindowscodecs