Changes imported from Abseil "staging" branch:

- f0a03a750a36dfbd7ab06d2913430ed5f988fd68 Add absl::RegisterSymbolizer() to mutex_nonprod.cc for AP... by Derek Mauro <dmauro@google.com>
  - f34a2ee35b4f6b321c570c51b0c381647176df63 Add the async signal-safe Symbolizer to Abseil. by Derek Mauro <dmauro@google.com>
  - 6a29ec2d6dc080691f6d32e1982201d1d173bdb3 Document preferred placement of ABSL_CONST_INIT attribute... by Abseil Team <absl-team@google.com>
  - 6f04ed6aa9c19bd717f0e8f422a97f3e3368cf30 Internal change. by Abseil Team <absl-team@google.com>
  - 0af9a330aff8fc0b41dcb3fe519930c36b01a9ef Declare absl::raw_logging_internal::SafeWriteToStderr in ... by Abseil Team <absl-team@google.com>
  - 223ff26745d31dfb4b59c36f3dee5441506af3c2 Fix ABSL_ARRAYSIZE() to handle rvalues. by Xiaoyi Zhang <zhangxy@google.com>

GitOrigin-RevId: f0a03a750a36dfbd7ab06d2913430ed5f988fd68
Change-Id: I491f9cc81ca3ee078fb737cbf8fa9bf6a730eee1

absl/base/attributes.h

@@ -543,11 +543,18 @@
 // not compile (on supported platforms) unless the variable has a constant
 // initializer. This is useful for variables with static and thread storage
 // duration, because it guarantees that they will not suffer from the so-called
-// "static init order fiasco".
+// "static init order fiasco".  Prefer to put this attribute on the most visible
+// declaration of the variable, if there's more than one, because code that
+// accesses the variable can then use the attribute for optimization.
 //
 // Example:
 //
-//   ABSL_CONST_INIT static MyType my_var = MakeMyType(...);
+//   class MyClass {
+//    public:
+//     ABSL_CONST_INIT static MyType my_var;
+//   };
+//
+//   MyType MyClass::my_var = MakeMyType(...);
 //
 // Note that this attribute is redundant if the variable is declared constexpr.
 #if ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)

absl/base/internal/raw_logging.cc

@@ -104,12 +104,6 @@ inline static bool VADoRawLog(char** buf, int* size,
 
 static constexpr int kLogBufSize = 3000;
 
-namespace absl {
-namespace raw_logging_internal {
-void SafeWriteToStderr(const char *s, size_t len);
-}  // namespace raw_logging_internal
-}  // namespace absl
-
 namespace {
 
 // CAVEAT: vsnprintf called from *DoRawLog below has some (exotic) code paths
@@ -188,12 +182,6 @@ void RawLogVA(absl::LogSeverity severity, const char* file, int line,
 
 namespace absl {
 namespace raw_logging_internal {
-
-// Writes the provided buffer directly to stderr, in a safe, low-level manner.
-//
-// In POSIX this means calling write(), which is async-signal safe and does
-// not malloc.  If the platform supports the SYS_write syscall, we invoke that
-// directly to side-step any libc interception.
 void SafeWriteToStderr(const char *s, size_t len) {
 #if defined(ABSL_HAVE_SYSCALL_WRITE)
   syscall(SYS_write, STDERR_FILENO, s, len);

absl/base/internal/raw_logging.h

@@ -74,6 +74,13 @@ namespace raw_logging_internal {
 void RawLog(absl::LogSeverity severity, const char* file, int line,
             const char* format, ...) ABSL_PRINTF_ATTRIBUTE(4, 5);
 
+// Writes the provided buffer directly to stderr, in a safe, low-level manner.
+//
+// In POSIX this means calling write(), which is async-signal safe and does
+// not malloc.  If the platform supports the SYS_write syscall, we invoke that
+// directly to side-step any libc interception.
+void SafeWriteToStderr(const char *s, size_t len);
+
 // compile-time function to get the "base" filename, that is, the part of
 // a filename after the last "/" or "\" path separator.  The search starts at
 // the end of the std::string; the second parameter is the length of the std::string.

absl/base/macros.h

@@ -46,7 +46,7 @@
 namespace absl {
 namespace macros_internal {
 template <typename T, size_t N>
-char (&ArraySizeHelper(T (&array)[N]))[N];
+auto ArraySizeHelper(const T (&array)[N]) -> char (&)[N];
 }  // namespace macros_internal
 }  // namespace absl
 #define ABSL_ARRAYSIZE(array) \