hwasan: Add __hwasan_init_static() function.

This function initializes enough of the runtime to be able to run
instrumented code in a statically linked executable. It replaces
__hwasan_shadow_init() which wasn't doing enough initialization for
instrumented code that uses either TLS or IFUNC to work.

Differential Revision: https://reviews.llvm.org/D57490

llvm-svn: 352816