Instrument std::string with ASAN contiguous container annotations.

[llvmbot]

Bugzilla Link	26380
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@mclow

Extended Description

__sanitizer_annotate_contiguous_container clearly mark used/unused portions of container storage and help catch out of bounds errors.

[llvmbot]

Proposed implementation: http://reviews.llvm.org/D12577

[AdvenamTacet]

There is a new, independent implementation, currently split into three revisions:

• Core implementation (long string and default allocator only) - https://reviews.llvm.org/D132769
• Turning on annotations for short strings - https://reviews.llvm.org/D147680
• Turn on annotations for all allocators (as in std::vector and std::deque) - https://reviews.llvm.org/D146214

That implementation is already somehow tested, but after that change it is required to build a separate libc++ dylibs with ASan, so we are waiting with landing for #33347 (we want to ship those dylibs with LLVM and we want driver to choose correct ones automatically, that should help with avoiding compatibility issues after that change).
While it is change "breaking ABI", ASan ABI is not stable.