[ASan] [SystemZ] Add -mbackchain to test cflags.

This is needed for proper operation of the fast unwinder, see the discussion
on D18895.

Differential Revision: http://reviews.llvm.org/D19898

llvm-svn: 269277

compiler-rt/test/asan/lit.cfg

@@ -73,6 +73,8 @@ clang_asan_static_cflags = (["-fsanitize=address",
                             "-fno-omit-frame-pointer",
                             "-fno-optimize-sibling-calls"] +
                             config.debug_info_flags + target_cflags)
+if config.target_arch == 's390x':
+  clang_asan_static_cflags.append("-mbackchain")
 clang_asan_static_cxxflags = config.cxx_mode_flags + clang_asan_static_cflags
 
 if config.asan_dynamic: