Changes imported from Abseil "staging" branch:

  - 1434dc58cc24e004531a09bcf1491773d9bf789e Copybara clang-format by Juemin Yang <jueminyang@google.com>
  - 6296f0f69b23d406a275b7ce2669ea3b18149bb7 Internal change for git pull request #31 by Juemin Yang <jueminyang@google.com>
  - 539940d88cfdf172b4b916d44225cc42839eeee7 Add internal-only ABSL_INTERNAL_HAVE_TSAN_INTERFACE macro. by Daniel Katz <katzdm@google.com>
  - bf85dda4ffdb4dd15084fb8b8db00281481dee90 Add missing pthread.h include to low_level_alloc.cc. by Derek Mauro <dmauro@google.com>

GitOrigin-RevId: 1434dc58cc24e004531a09bcf1491773d9bf789e
Change-Id: I68d6957b0cac32020e4e34dca3243f2f270a4b9c

CONTRIBUTING.md

@@ -48,7 +48,7 @@ will be expected to conform to the style outlined
 
 *   Don't fix code style and formatting unless you are already changing that
     line to address an issue. Formatting of modified lines may be done using
-    `git clang-format`. PRs with irrelevant changes won't be merged. If
+   `git clang-format`. PRs with irrelevant changes won't be merged. If
     you do want to fix formatting or style, do that in a separate PR.
 
 *   Unless your PR is trivial, you should expect there will be reviewer comments

absl/base/internal/low_level_alloc.cc

@@ -30,6 +30,7 @@
 #ifndef ABSL_LOW_LEVEL_ALLOC_MISSING
 
 #ifndef _WIN32
+#include <pthread.h>
 #include <signal.h>
 #include <sys/mman.h>
 #include <unistd.h>

absl/base/internal/tsan_mutex_interface.h

@@ -19,7 +19,22 @@
 #ifndef ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
 #define ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
 
-#ifdef THREAD_SANITIZER
+// ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+// Macro intended only for internal use.
+//
+// Checks whether LLVM Thread Sanitizer interfaces are available.
+// First made available in LLVM 5.0 (Sep 2017).
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+#error "ABSL_INTERNAL_HAVE_TSAN_INTERFACE cannot be directly set."
+#endif
+
+#if defined(THREAD_SANITIZER) && defined(__has_include)
+#if __has_include(<sanitizer/tsan_interface.h>)
+#define ABSL_INTERNAL_HAVE_TSAN_INTERFACE 1
+#endif
+#endif
+
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
 #include <sanitizer/tsan_interface.h>
 
 #define ABSL_TSAN_MUTEX_CREATE __tsan_mutex_create