G++ 6.0 asserts that the "this" pointer is non-null for member
functions.
Refactor methods that check if "this" is non-null to resolve this.
winsup/cygwin/ChangeLog:
external.cc (cygwin_internal): Check for a null pinfo before calling
cmdline.
fhandler_dsp.cc (Audio::blockSize): Make static.
Rename without-mingw-progs to with-cross-bootstrap, since it now
disables additional checks that are problematic for cross-compilers.
When cross-compiling a toolchain targeting cygwin, building cygwin1.dll
requires libgcc.
However, building libgcc requires the cygwin headers to be
installed.
