Unbreak build with base libstdc++ on i386 and powerpc
std::abs(int64_t) for 32bit archs or std::llabs are not available in
base libstdc++ or before 10.0-RELEASE (r255294) for libstdc++ in
lang/gcc47 and earlier (libstdc++/54686). To avoid the build error use
mozilla::Abs which implements overloads for all signed natural types
but has unsigned return value.
This change won't be requried for Firefox 36 et al.
PR: 196772
Reported by: many
Patch by: bar (initial version)
Obtained from: https://github.com/mozilla/gecko-dev/commit/e664fe8
Approved by: flo (mentor)
MFH: 2015Q1