dev-libs/libx86: keyword 1.1-r4 for -ppc, -riscv, -sparc

Fails to build, see Bug #764656. Nb. both BSD ports and most (all?)
other Linux distros have this package only support amd64 and x86, and
back when the upstream Web site still existed they only mentioned
compatibility with amd64, x86 and alpha. On Gentoo it apparently builds
on arm as well, that said it's not clear whether it actually works there
- on the one hand there doesn't seem to have been any run-time testing
involved in arm keywording, on the other the keywording bug mentions
Debian patches yet Debian hasn't had libx86 arm packages at least since
Stretch.

Signed-off-by: Marek Szuba <marecki@gentoo.org>

dev-libs/libx86/libx86-1.1-r4.ebuild

@@ -11,7 +11,7 @@ SRC_URI="https://www.codon.org.uk/~mjg59/${PN}/downloads/${P}.tar.gz"
 
 LICENSE="BSD"
 SLOT="0"
-KEYWORDS="amd64 ~arm x86"
+KEYWORDS="amd64 ~arm -ppc -riscv -sparc x86"
 IUSE="static-libs"
 
 src_prepare() {