Use `make STATIC=1` to build a static library.
Some language ecosystems, like those of Rust, have a convention of
static linking in order to make binaries easier to distribute. In those
environments, this feature helps libui fit in more easily.
In order to prevent internal symbols from linking, we first create an
intermediate object file with `ld -r` and strip private symbols from it
before using `ar` to create the library.
1) cvtres is no longer used directly. MSDN says to send the .res files to link.exe; that runs cvtres for us (at least it seems to, accoring to Google results for error LNK1158). It'll also avoid some of the weird warnings in cvtres, like CVT4001.
2) (and more important, but it depended on 1) Command-line switches are now passed using - instead of /. This is because some versions of MinGW are buggy and treat anything that starts with a / as a MSYS filename that needs to be converted to a Windows pathname.
Update #16.