Provide storage for `true_type::value` and `false_type::value`.

[delcypher]

Summary

This fixes linker errors that occurs when the
sanitizer_type_traits_test.cc is built without optimizations.

The error occurs because the test tries to take a reference.
A possible workaround is to give the GTest macros take boolean rvalues
by doing something like:

ASSERT_TRUE(bool(is_same<uptr, uptr>::value));

However this only hides the problem. Unfortunately Using constexpr
won't fix the problem unless we are using C++17.

[vitalybuka]

lib/sanitizer_common/sanitizer_type_traits.cc

18

I guess we can avoid cc file if you use constexpr in the header file.

[delcypher]

lib/sanitizer_common/sanitizer_type_traits.cc

18

@vitalybuka I tried that. Unfortunately I still get link errors.

See https://stackoverflow.com/questions/8452952/c-linker-error-with-class-static-constexpr .

An alternative to this patch to just change the test that causes the problem to something like

ASSERT_TRUE(bool(is_same<uptr, uptr>::value));
`

This avoids taking a reference to is_same<T,U>::value and instead constructs a temporary value from it. The ASSERT_TRUE macro then takes a reference to it.

I'm not sure which is better. Changing the test just hides the issue (it will occur again if anyone tries to take a reference to is_same<T,U>::value). However this patch bloats the code for the purpose of a single test, which isn't great either.

Let me know, which you'd prefer.

[vitalybuka]

LGTM as is

lib/sanitizer_common/sanitizer_type_traits.cc

20

please add empty lines to separate namemespace {}

[delcypher]

Adding spacing above and below declarations in namespace.

lib/sanitizer_common/CMakeLists.txt

set(SANITIZER_SOURCES_NOTERMINATION
   sanitizer_procmaps_mac.cc
   sanitizer_procmaps_solaris.cc
   sanitizer_rtems.cc
   sanitizer_solaris.cc
   sanitizer_stoptheworld_mac.cc
   sanitizer_suppressions.cc
   sanitizer_tls_get_addr.cc
   sanitizer_thread_registry.cc
+  sanitizer_type_traits.cc
   sanitizer_win.cc)
 
 if(UNIX AND NOT APPLE AND NOT OS_NAME MATCHES "SunOS")
   list(APPEND SANITIZER_SOURCES_NOTERMINATION
     sanitizer_linux_x86_64.S)
   list(APPEND SANITIZER_SOURCES_NOTERMINATION
     sanitizer_linux_mips64.S)
 endif()

lib/sanitizer_common/sanitizer_type_traits.cc

+//===-- sanitizer_type_traits.cc --------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Implements a subset of C++ type traits. This is so we can avoid depending
+// on system C++ headers.
+//
+//===----------------------------------------------------------------------===//
+#include "sanitizer_type_traits.h"
+
+namespace __sanitizer {
+
+const bool true_type::value;
+const bool false_type::value;
+
+}  // namespace __sanitizer