[ASan] get rid of ASAN_USE_EXTERNAL_SYMBOLIZER compiler def in favor of __asan_set_symbolize_callback interface function. Now the user doesn't have to recompile ASan runtime to provide its own symbolizer

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@162358 91177308-0d34-0410-b5e6-96231b3b80d8
8 files changed