[sanitizer_common] Check 'demangle' flag in StripFunctionName and DemangleFunctionName

[melver]

Summary

To allow getting the original stack trace.

Depends on D151319

compiler-rt/lib/sanitizer_common/sanitizer_stacktrace_printer.cpp

 //===-- sanitizer_common.cpp ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file is shared between sanitizers' run-time libraries.
 //
 //===----------------------------------------------------------------------===//
 
 #include "sanitizer_stacktrace_printer.h"
+
 #include "sanitizer_file.h"
+#include "sanitizer_flags.h"
 #include "sanitizer_fuchsia.h"
 
 namespace __sanitizer {
 
 const char *StripFunctionName(const char *function) {
+  if (!common_flags()->demangle)
+    return function;
   if (!function)
     return nullptr;
   auto try_strip = [function](const char *prefix) -> const char * {
     const uptr prefix_len = internal_strlen(prefix);
     if (!internal_strncmp(function, prefix, prefix_len))
       return function + prefix_len;
     return nullptr;
   };
   if (SANITIZER_APPLE) {
     if (const char *s = try_strip("wrap_"))
       return s;
   } else {
     if (const char *s = try_strip("__interceptor_"))
       return s;
   }
   return function;
 }
 
 // sanitizer_symbolizer_markup.cpp implements these differently.
 #if !SANITIZER_SYMBOLIZER_MARKUP
 
 static const char *DemangleFunctionName(const char *function) {
-  if (!function) return nullptr;
+  if (!common_flags()->demangle)
+    return function;
+  if (!function)
+    return nullptr;
 
   // NetBSD uses indirection for old threading functions for historical reasons
   // The mangled names are internal implementation detail and should not be
   // exposed even in backtraces.
 #if SANITIZER_NETBSD
   if (!internal_strcmp(function, "__libc_mutex_init"))
     return "pthread_mutex_init";
   if (!internal_strcmp(function, "__libc_mutex_lock"))