src: add define of ENOMSG for MinGW
src: add define of ENOMSG for MinGW

MinGW lacks ENOMSG until version 6.0.0 (Fedora 31).

Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>
Signed-off-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

nertpinx/libvirt,libvirt/libvirt,olafhering/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,crobinso/libvirt,crobinso/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,zippy2/libvirt,jardasgit/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,jardasgit/libvirt,jfehlig/libvirt,olafhering/libvirt,nertpinx/libvirt,crobinso/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,nertpinx/libvirt,crobinso/libvirt,jardasgit/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt