strerror: Add Curl_winapi_strerror for Win API specific errors

- In all code call Curl_winapi_strerror instead of Curl_strerror when the error code is known to be from Windows GetLastError. Curl_strerror prefers CRT error codes (errno) over Windows API error codes (GetLastError) when the two overlap. When we know the error code is from GetLastError it is more accurate to prefer the Windows API error messages. Reported-by: Richard Alcock Fixes #4550 Closes #4581

Author: jay