Changes imported from Abseil "staging" branch:

- 0320844dcd8219965647f86db7c6c7296e40e41e Introduce internal macros for inline variable emulation s... by Matt Calabrese <calabrese@google.com>
  - 85197d0105805e6aab3a0a648351cb1582a61be0 Internal change. by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: 0320844dcd8219965647f86db7c6c7296e40e41e
Change-Id: I7dce37f6839ff099462951059a9047c5c9377638

absl/utility/utility.h

@@ -45,6 +45,7 @@
 #include <utility>
 
 #include "absl/base/config.h"
+#include "absl/base/internal/inline_variable.h"
 #include "absl/base/internal/invoke.h"
 #include "absl/meta/type_traits.h"
 
@@ -155,7 +156,8 @@ using std::in_place;
 // `absl::optional`, designed to be a drop-in replacement for C++17's
 // `std::in_place_t`.
 struct in_place_t {};
-extern const in_place_t in_place;
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(in_place_t, in_place, {});
 
 #endif  // ABSL_HAVE_STD_OPTIONAL