hg: jdk/sandbox: Cleanup bootstrap on cygwin.

[magnus.ihse.bursie at oracle.com]

Changeset: 779418cddecf
Author:    ihse
Date:      2020-06-06 00:57 +0200
URL:       https://hg.openjdk.java.net/jdk/sandbox/rev/779418cddecf

Cleanup bootstrap on cygwin.

! make/autoconf/basic_tools.m4
! make/autoconf/basic_windows.m4
! make/autoconf/help.m4