1. Remove unused variable `fallible` to fix warning-as-error in non-unified build on OS X. In bug 441324 comment 8, bsmedberg recommended removing the extern declaration of `fallible`, but the cpp file's definition of `fallible` was not removed. > memory/mozalloc/mozalloc.cpp:227:18: error: unused variable 'fallible' [-Werror,-Wunused-const-variable] 2. Mark mozalloc as FAIL_ON_WARNINGS for clang. mozalloc can't be FAIL_ON_WARNINGS for gcc yet because of the following warning about mozalloc.cpp's definition of abort() not being noreturn. Fixing that warning is nontrivial. mozalloc_abort.h has a comment saying noreturn breaks mozalloc_abort's stack traces on ARM. > memory/mozalloc/mozalloc_abort.cpp:76:1: warning: 'noreturn' function does return [enabled by default]