mingw: enable using strcasecmp()

[vszakats]

This will make the Features: list sorted case-insensitively, bringing output in-line with *nix builds.

[jay]

You could get rid of HAVE_STRCASECMP as well and replace strcasecmp with curl_strequal

[bagder]

The only current use of strcasecmp() is src/tool_help.c which uses the function as input to qsort(). This means curl_strequal() is not a simple drop-in replacement as they differ in return codes, in particular when there's not a match.

[jay]

This means curl_strequal() is not a simple drop-in replacement as they differ in return codes, in particular when there's not a match.

ah didn't realize that.. disregard then