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/base/BUILD.bazel

@@ -128,6 +128,7 @@ cc_library(
     name = "base_internal",
     hdrs = [
         "internal/identity.h",
+        "internal/inline_variable.h",
         "internal/invoke.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
@@ -257,6 +258,22 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "inline_variable_test",
+    size = "small",
+    srcs = [
+        "inline_variable_test.cc",
+        "inline_variable_test_a.cc",
+        "inline_variable_test_b.cc",
+        "internal/inline_variable_testing.h",
+    ],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":base_internal",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "invoke_test",
     size = "small",