Slightly tangential, and while I know nothing about the implementation details of the SQLPAL, the SSCLI (and later CLR/CoreCLR) took the same approach to port Windows based code to Unixes [1] and makes for interesting code reading. For e.g. The SSCLI PAL's implementation of SEH [2].

[1] https://github.com/lewischeng-ms/sscli/tree/master/pal/unix

[2] https://github.com/lewischeng-ms/sscli/blob/adbd6bbad0816f65...