Support, IR, ADT: Check nullptr after allocation with malloc/realloc or calloc

As a follow up of the bad alloc handler patch, this patch introduces nullptr checks on pointers returned from the
malloc/realloc/calloc functions.  In addition some memory size assignments  are moved behind the allocation
of the corresponding memory to fulfill exception safe memory management (RAII).

patch by Klaus Kretzschmar

Differential Revision: https://reviews.llvm.org/D35414

llvm-svn: 308576