[compiler-rt][asan] Add support for desallocation of unhandled pointers

Summary: On windows 10, the ucrt DLL is performing allocations before the function hooking and there are multiple allocations not handled by Asan. When a free occur at the end of the process, asan is reporting desallocations not malloc-ed.

Reviewers: rnk, kcc

Reviewed By: rnk, kcc

Subscribers: kcc, llvm-commits, kubamracek, chrisha, dberris

Differential Revision: https://reviews.llvm.org/D25946

llvm-svn: 295730