Changes imported from Abseil "staging" branch:

- db061dd2b795837e6154be0991077ca5a03ec471 Release the async-signal safe demangler as an internal im... by Derek Mauro <dmauro@google.com>
  - 310440eb33d946df79d26bf1edf795f6a0b466b9 Use static_cast to constrain nanoseconds to int range, av... by Abseil Team <absl-team@google.com>

GitOrigin-RevId: db061dd2b795837e6154be0991077ca5a03ec471
Change-Id: Ibc1bc1db355a48115451da5ce88d66a1f6e1a182

absl/debugging/BUILD.bazel

@@ -64,10 +64,34 @@ cc_library(
     deps = [
         "//absl/base",
         "//absl/base:dynamic_annotations",
+    ],
+)
+
+cc_library(
+    name = "demangle_internal",
+    srcs = ["internal/demangle.cc"],
+    hdrs = ["internal/demangle.h"],
+    copts = ABSL_DEFAULT_COPTS,
+    deps = [
+        "//absl/base",
         "//absl/base:core_headers",
     ],
 )
 
+cc_test(
+    name = "demangle_test",
+    srcs = ["internal/demangle_test.cc"],
+    copts = ABSL_TEST_COPTS,
+    deps = [
+        ":demangle_internal",
+        ":stack_consumption",
+        "//absl/base",
+        "//absl/base:core_headers",
+        "//absl/memory",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_library(
     name = "leak_check",
     srcs = select({