Export of internal Abseil changes.

--
821196cfb2a3b943ffdc4c9e75daec92d7ffb28b by Abseil Team <absl-team@google.com>:

Performance improvements

PiperOrigin-RevId: 212668992

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704858e2e767016bad27d53eec01d9d48e546b23 by Abseil Team <absl-team@google.com>:

Low-level Portability enchancements for Abseil Mutex on WebAssembly.

Emscripten Pthreads do not use signals, so remove use of pthread_sigmask or
other async-signal-safe related handling code.

PiperOrigin-RevId: 212527958

--
be3e38cb4d493b755132d20c8c2d1a51e45d5449 by Jon Cohen <cohenjon@google.com>:

Internal change.

PiperOrigin-RevId: 212523797
GitOrigin-RevId: 821196cfb2a3b943ffdc4c9e75daec92d7ffb28b
Change-Id: I5694e23e4e09364a15dd6fc4e2e3f15e38835687

absl/strings/internal/str_format/extension.h

@@ -18,6 +18,7 @@
 #define ABSL_STRINGS_INTERNAL_STR_FORMAT_EXTENSION_H_
 
 #include <limits.h>
+#include <cstddef>
 #include <cstring>
 #include <ostream>
 
@@ -307,7 +308,12 @@ class ConversionSpec {
  public:
   Flags flags() const { return flags_; }
   LengthMod length_mod() const { return length_mod_; }
-  ConversionChar conv() const { return conv_; }
+  ConversionChar conv() const {
+    // Keep this field first in the struct . It generates better code when
+    // accessing it when ConversionSpec is passed by value in registers.
+    static_assert(offsetof(ConversionSpec, conv_) == 0, "");
+    return conv_;
+  }
 
   // Returns the specified width. If width is unspecfied, it returns a negative
   // value.
@@ -324,9 +330,9 @@ class ConversionSpec {
   void set_left(bool b) { flags_.left = b; }
 
  private:
+  ConversionChar conv_;
   Flags flags_;
   LengthMod length_mod_;
-  ConversionChar conv_;
   int width_;
   int precision_;
 };