gc: malloc() and calloc() overflows

Multiple integer overflows in the 1 GCgenericmalloc and 2 calloc functions in malloc.c, and the 3 GCgenericmallocignoreoffpage function in mallocx.c in Boehm-Demers-Weiser GC libgc before 7.2 make it easier for context-dependent attackers to perform memory-related attacks such as buffer overflows...