sys-libs/newlib: Migrate CROSSCOMPILE_OPTS=headers-only -> USE=headers-only
CROSSCOMPILE_OPTS is a USE_EXPAND of a single item: headers-only.
Convert it to a global USE flag instead.
Mechanical ebuild rename done as:
$ sed -e 's@crosscompile_opts_headers-only@headers-only@g' \
-i $(git grep -l headers-only)
'headers-only' flag is used by crossdev to bootstrap stage1 compiler
before libc is available.
crossdev switched to USE=headers-only in =sys-devel/crossdev-
20171230.
Bug: https://bugs.gentoo.org/642712
Package-Manager: Portage-2.3.19, Repoman-2.3.6