[libcxxabi] Add support for running libc++abi tests with sanitizers

[EricWF]

Summary

Add support for LLVM_USE_SANITIZER to the libc++abi tests. Currently, if libc++abi is configured with LLVM_USE_SANITIZER then none of the tests will pass.

[danalbert]

LGTM.

test/lit.cfg

 library_paths = ['-L' + libcxxabi_obj_root + '/lib']
 compile_flags = ['-std=c++11']
 
+
+san = lit_config.params.get('llvm_use_sanitizer', None)
+if san is None:
+    san = getattr(config, 'llvm_use_sanitizer', None)
+if san:
+    if not sys.platform.startswith('freebsd'):
+        link_flags += ['-ldl']
+    if san == 'Address':
+        compile_flags += ['-fsanitize=address']
+        config.available_features.add('asan')
+    elif san == 'Memory' or san == 'MemoryWithOrigins':
+        compile_flags += ['-fsanitize=memory']
+        config.available_features.add('msan')
+        if san == 'MemoryWithOrigins':
+            compile_flags += ['-fsanitize-memory-track-origins']
+    elif san == 'Undefined':
+        compile_flags += ['-fsanitize=undefined',
+                          '-fno-sanitize=vptr,function',
+                          '-fno-sanitize-recover']
+        config.available_features.add('ubsan')
+    else:
+        lit_config.fatal('unsupported value for '
+                         'llvm_use_sanitizer: {0}'.format(san))
+
+
 # Configure extra linker parameters.
 exec_env = {}
 if sys.platform == 'darwin':

test/lit.site.cfg.in

 config.enable_shared         = @LIBCXXABI_ENABLE_SHARED@
 config.libcxx_includes       = "@LIBCXXABI_LIBCXX_INCLUDES@"
 config.llvm_unwinder         = @LIBCXXABI_USE_LLVM_UNWINDER@
+config.llvm_use_sanitizer    = "@LLVM_USE_SANITIZER@"
 
 # Let the main config do the real work.
 lit_config.load_config(config, "@LIBCXXABI_SOURCE_DIR@/test/lit.cfg")