[llvm] [Support][Cygwin] Fix handling of Process symbol lookup. (PR #143072)

[via llvm-commits]

jeremyd2019 wrote:

cc @mstorsjo

this seemed less invasive than trying to use `this` as the `Process` handle, as seems to be done on the Windows/DynamicLibrary.inc side of things (since we don't have to do any additional special handling in the Unix/DynamicLibrary.inc side beyond using `RTLD_DEFAULT` instead of the executable's handle for `Process`)

https://github.com/llvm/llvm-project/pull/143072