Ability to optionally depend on Abseil plus upstream of 183716547

BUILD.bazel

@@ -46,6 +46,12 @@ config_setting(
     values = {"cpu": "x64_windows_msvc"},
 )
 
+config_setting(
+    name = "has_absl",
+    values = {"define": "absl=1"},
+)
+
+
 # Google Test including Google Mock
 cc_library(
     name = "gtest",
@@ -88,6 +94,20 @@ cc_library(
             "-pthread",
         ],
     }),
+    defines = select ({
+        ":has_absl": [
+        "GTEST_HAS_ABSL=1",
+        ],
+        "//conditions:default": [],
+    }
+    ),
+    deps = select ({
+        ":has_absl": [
+        "@com_google_absl//absl/types:optional",
+        ],
+        "//conditions:default": [],
+    }
+    )
 )
 
 cc_library(