Got detected by gentoo's QA preinstall hook:
 * RWX --- --- usr/lib/ghc-7.10.1/rts/libffi.so.6.0.2
 * RWX --- --- usr/lib/ghc-7.10.1/rts/libffi.so
 * RWX --- --- usr/lib/ghc-7.10.1/rts/libffi.so.6
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_p.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_l.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_debug.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_thr.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_thr_debug.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_thr_l.a:win32.o
 * !WX --- --- usr/lib/ghc-7.10.1/rts/libCffi_thr_p.a:win32.o

Signed-off-by: Sergei Trofimovich <siarheit@google.com>

Test Plan: built ghc-7.10.1 binary and checked stacks as NX

Reviewers: rwbarton, hvr, austin

Reviewed By: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D764

GHC Trac Issues: #10208