diagnostics: Don't hardcode auto_enable_urls to false for mingw hosts

diagnostics: Don't hardcode auto_enable_urls to false for mingw hosts

Windows terminal and mintty both have support for link escape sequences, and so
auto_enable_urls shouldn't be hardcoded to false. For older versions of the
windows console, mingw_ansi_fputs's console API translation logic does mangle
these sequences, but there's nothing useful it could do even if this weren't
the case, so check if the ansi escape sequences are supported at all.

conhost.exe doesn't support link escape sequences, but printing them does not
cause any problems.

gcc/ChangeLog:
	* diagnostic-color.cc (auto_enable_urls): Don't hardcode to return
	false on mingw hosts.
	(auto_enable_urls): Return true if console
	supports ansi escape sequences.

Signed-off-by: Peter Damianov <peter0x44@disroot.org>