rename WinHTTP CMake target (#1240)

# Pull Request Checklist

Please leverage this checklist as a reminder to address commonly occurring feedback when submitting a pull request to make sure your PR can be reviewed quickly:

See the detailed list in the [contributing guide](https://github.com/Azure/azure-sdk-for-cpp/blob/master/CONTRIBUTING.md#pull-requests).

- [x] [C++ Guidelines](https://azure.github.io/azure-sdk/cpp_introduction.html)
- [x] Doxygen docs
- [x] Unit tests
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sdk/core/azure-core/CMakeLists.txt

@@ -126,8 +126,7 @@ if(BUILD_TRANSPORT_CURL)
   target_link_libraries(azure-core PRIVATE CURL::libcurl)
 endif()
 if(BUILD_TRANSPORT_WINHTTP)
-  SET(WIN_HTTP_LIB Winhttp.lib)
-  target_link_libraries(azure-core PRIVATE ${WIN_HTTP_LIB})
+  target_link_libraries(azure-core PRIVATE winhttp)
 endif()
 
 get_az_version("${CMAKE_CURRENT_SOURCE_DIR}/inc/azure/core/version.hpp")