[asan] fill first 4K of malloc-ed memory with garbage, implement flags max_malloc_fill_size and malloc_fill_byte

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@178757 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] nuke the old unused allocator code

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@178758 91177308-0d34-0410-b5e6-96231b3b80d8