[Sanitizer] Bump macOS deployment target for sanitizer unit test binary to support...

[Sanitizer] Bump macOS deployment target for sanitizer unit test binary to support C++17 requirements.

This patch fixes a test failure on Apple caused by changing standard to c++17.
sanitizer_allocator_test.cpp requires language features introducied in 10.13 for c++17.
After initial investigation, it was not clear how to add this flag to a single file:
https://reviews.llvm.org/D133878

Becuase of this, we have upped the min version of this test suite to 10.13, the min version necessary to support necessary language features.

We felt this was a better option than upping the min version of the product to support a single test.
We are raising deployment target for a single test suite, rather than the product.

Differential Revision: https://reviews.llvm.org/D134091

rdar://98737270