Backport Wikipedia crashfix for clang 3.5

PR: 196802
Reported by: dumbbell
Obtained from: https://github.com/mozilla/gecko-dev/commit/87f367b
Obtained from: https://github.com/mozilla/gecko-dev/commit/c97894b (esr31 version)
Differential Revision: https://reviews.freebsd.org/D1568
Approved by: flo (mentor)
MFH: 2015Q1