dev-embedded/sdcc: require sdbinutils for every port, bug #678354

dev-embedded/sdcc: require sdbinutils for every port, bug #678354

Top-level Makefile unconditionally pulls in sdcc-binutils as a dependency.
If being opted out explicitly the build always fails as:
    make -j5 -s
    make[1]: *** No targets specified and no makefile found.  Stop.
    make: *** [Makefile:147: sdcc-sdbinutils] Error 2

Fix it by effectively requiring IUSE=sdbinutils for each port.

Reported-by: email200202@yahoo.com
Closes: https://bugs.gentoo.org/678354
Package-Manager: Portage-2.3.61, Repoman-2.3.12
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>