cpprest_compat breaks cURL header when building with Clang 14

`#define dllimport` inside [cpprest_compat.h](https://.com/microsoft/cpprestsdk/blob/80444805898842f7e5c62b256337c0897eb254bb/Release/include/cpprest/details/cpprest_compat.h) breaks [curl.h](https://.com/curl/curl/blob/bfbde883af33397943df68a3ae01847a634d33bf/include/curl/curl.h#L120) on Clang 14.

See minimized example here: [godbolt](https://godbolt.org/z/T6nxGY4cz)

The issue was initially [reported to LLVM](https://.com/llvm/llvm-project/issues/53269).
The LLVM issue was closed. For the reason, see these comments: [comment1](https://.com/llvm/llvm-project/issues/53269#issuecomment-1158813473) and [comment2](https://.com/llvm/llvm-project/issues/53269#issuecomment-1161732686).

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