Bug 1134923 removed the use of those functions in gecko, and left some
for the XPCOM standalone glue. The XPCOM standalone glue was severely
stripped down in bug 1306327, with the effect of removing the
implementation for those functions.
The remains in nsXPCOM.h are:
XPCOM_API(void*) NS_Alloc(size_t aSize);
XPCOM_API(void*) NS_Realloc(void* aPtr, size_t aSize);
XPCOM_API(void) NS_Free(void* aPtr);
With no implementation left, the first arm is never actually used, and
the second arm means every remaining use of those functions in the tree
is a macro expansion to one of moz_xmalloc, moz_xrealloc or free.
