Re: 2.23.11 build failure on cygwin #2

[Masamichi Hosoda]

> second issue building on Cygwin
> 
> The Cygwin headers are very picky and the "-std=c++14" cause some not
> standard calls to fail compilation due to the reduced scope.
> 
> The solution is to remove the "-std=c++14" or to replace with
> "-std=gnu++14"

This fix also contained in the following merge request.
https://gitlab.com/lilypond/lilypond/-/merge_requests/1554