Previously, the TSan runtime only required libdispatch on Darwin, which
required no explicit linker flags, because libdispatch is always
provided by the system (libSystem).
Now, the TSan runtime also has a link-time dependency on libdispatch on
Linux, where libdispatch (and the blocks runtime) is just another
library. We therefore need to specify them as additonal linker options.
This change allows the swift driver to link the ubsan runtime if
`-sanitize=undefined` is specified.
This is useful for sanitizing linked Objective-C code.
With this patch different sanitizers (tsan/asan) will be enabled or
disabled on the driver level on a particular OS depending on whether
the required library is present.
The current patch only supports Darwin architectures, but Linux support
should not be hard to add.
ASan allows to catch and diagnose memory corruption errors, which are possible
when using unsafe pointers.
This patch introduces a new driver/frontend option -sanitize=address to enable
ASan. When option is passed in, the ASan llvm passes will be turned on and
all functions will gain SanitizeAddress llvm attribute.
