definint dllimport is *bad* and breaks clang, and since this is in maintaince mode they aren't going to fix it.  Refs:

microsoft/cpprestsdk#1710
llvm/llvm-project#53269

- **[cpprestsdk] fix clang build on new zlib**
- **./vcpkg x-add-version --all**


Defining `dllimport` is *bad* and breaks clang, and since this is in
maintaince mode they aren't going to fix it.

This had the ability to blow up projects before, but newer zlib versions
use `__has_declspec_attribute`, so that makes it impossible to even
_build_ cpprestsdk on systems like these (I'm on Fedora 40).

Refs:

microsoft/cpprestsdk#1710
llvm/llvm-project#53269

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