Now that newlib.hin has been brought up to date and all of its defines
are produced by configure, we can switch it to using autoheader without
manual editing. This relies on a few pieces:
* Moving the header & footer into configure.ac via AH_TOP & AH_BOTTOM.
* Running a post-process step on newlib.h to delete all the defines we
didn't export ourselves. Basically, anything without a _ prefix.
This will leave behind some spurious comments in newlib.h related to
the defines we filtered out, but should be harmless, so it's probably
not worth the effort to construct a more complicated sed expression to
also strip those out.
git://sourceware.org / newlib-cygwin.git / commit