[asan] instrument memory accesses with unusual sizes

This patch makes asan instrument memory accesses with unusual sizes (e.g. 5 bytes or 10 bytes), e.g. long double or
packed structures.
Instrumentation is done with two 1-byte checks
(first and last bytes) and if the error is found
__asan_report_load_n(addr, real_size) or
__asan_report_store_n(addr, real_size)
is called.

Also, call these two new functions in memset/memcpy
instrumentation.

asan-rt part will follow.

llvm-svn: 175507