[ASan] Use debuginfo for symbolization.

Hint: Looking here because your manual invocation of something in
'check-asan' broke? You need a new symbolizer (after D123538).

An upcoming patch will remove the internal metadata for global
variables. With D123534 and D123538, clang now emits DWARF debug info
for constant strings (the only global variable type it was missing), and
llvm-symbolizer is now able to symbolize all global variable addresses
(where previously it wouldn't give you the file:line information).

Move ASan's runtime over from the internal metadata to DWARF.

Differential Revision: https://reviews.llvm.org/D127552