Fixes CVE-2017-15107, but also contains some one incompatible changes.

Backported patches [1][2] that add support for
llvm-libunwind[3] on ppc64le.

[1] dc25db1eb7a3cbe5c1b58f5225606efe9218ccd0
[2] 2b4c5e067b7259ae5d60553c62e309a1780df570
[3] https://github.com/llvm-mirror/libunwind

fixes #8701

CVE-2018-5125: Memory safety bugs fixed in Firefox 59 and Firefox ESR
               52.7
CVE-2018-5127: Buffer overflow manipulating SVG animatedPathSegList
CVE-2018-5129: Out-of-bounds write with malformed IPC messages
CVE-2018-5130: Mismatched RTP payload type can trigger memory corruption
CVE-2018-5131: Fetch API improperly returns cached copies of
               no-store/no-cache resources
CVE-2018-5144: Integer overflow during Unicode conversion
CVE-2018-5145: Memory safety bugs fixed in Firefox ESR 52.7