Support Fuchsia target builds.

The Fuchsia team has been using either fork branches
(https://fuchsia.googlesource.com/third_
party/github.com/google/googletest/+/refs/heads/sandbox/fuchsia_bazel_sdk)
or patch files
(https://cs.opensource.google/fuchsia/fuchsia/+/main:build/bazel/patches/googletest/fuchsia-support.bundle)
to support googletest-based tests that run against a Fuchsia target device.

As our SDK is maturing and @platforms//os:fuchsia constraint has been added
for a while now, upstream Fuchsia gtest support to reduce technical debt and
overhead.

This change is noop for non-fuchsia platform builds.

PiperOrigin-RevId: 606843739
Change-Id: I61e0eb9c641f288d7ae57354fc0b484fce013223

BUILD.bazel

@@ -56,6 +56,12 @@ config_setting(
     constraint_values = ["@platforms//os:openbsd"],
 )
 
+# NOTE: Fuchsia is not an officially supported platform.
+config_setting(
+    name = "fuchsia",
+    constraint_values = ["@platforms//os:fuchsia"],
+)
+
 config_setting(
     name = "msvc_compiler",
     flag_values = {
@@ -147,6 +153,17 @@ cc_library(
             "@com_googlesource_code_re2//:re2",
         ],
         "//conditions:default": [],
+    }) + select({
+        # `gtest-death-test.cc` has `EXPECT_DEATH` that spawns a process,
+        # expects it to crash and inspects its logs with the given matcher,
+        # so that's why these libraries are needed.
+        # Otherwise, builds targeting Fuchsia would fail to compile.
+        ":fuchsia": [
+            "@fuchsia_sdk//pkg/fdio",
+            "@fuchsia_sdk//pkg/syslog",
+            "@fuchsia_sdk//pkg/zx",
+        ],
+        "//conditions:default": [],
     }),
 )