Indirection for the Gradle version.

Change-Id: I1bbbc9cbc5cbea38bab972d22b68870021044383
Test: automated tests pass.

BUILD

@@ -2,46 +2,41 @@
 # Gradle 2.14.1
 #######
 
+# do not use directly. Use //tools/base/build-system:gradle
 filegroup(
-    name = "gradle-2.14.1",
+    name = "gradle-distrib-2.14.1",
     srcs = ["gradle-2.14.1-bin.zip"],
-    visibility = ["//visibility:public"],
+    visibility = ["//tools/base/build-system:__pkg__"],
 )
 
 # gradle-api jar, as generated by gradle when using the gradleApi() magic dependency.
-java_import(
+# do not use directly. Use
+# //tools/base/build-system:gradle-api_neverlink
+# //tools/base/build-system:gradle-api
+filegroup(
     name = "gradle-api-2.14.1",
-    jars = ["gradle-api-2.14.1.jar"],
-    visibility = ["//visibility:public"],
-)
-
-java_library(
-    name = "gradle-api-2.14.1_neverlink",
-    neverlink = 1,
-    exports = [":gradle-api-2.14.1"],
-    visibility = ["//visibility:public"],
+    srcs = ["gradle-api-2.14.1.jar"],
+    visibility = ["//tools/base/build-system:__pkg__"],
 )
 
 #######
 # gradle 3.2
 #######
 
+# do not use directly. Use //tools/base/build-system:gradle
 filegroup(
-    name = "gradle-3.2",
+    name = "gradle-distrib-3.2",
     srcs = ["gradle-3.2-bin.zip"],
-    visibility = ["//visibility:public"],
+    visibility = ["//tools/base/build-system:__pkg__"],
 )
 
 # gradle-api jar, as generated by gradle when using the gradleApi() magic dependency.
-java_import(
+# do not use directly. Use
+# //tools/base/build-system:gradle-api_neverlink
+# //tools/base/build-system:gradle-api
+filegroup(
     name = "gradle-api-3.2",
-    jars = ["gradle-api-3.2.jar"],
-    visibility = ["//visibility:public"],
+    srcs = ["gradle-api-3.2.jar"],
+    visibility = ["//tools/base/build-system:__pkg__"],
 )
 
-java_library(
-    name = "gradle-api-3.2_neverlink",
-    neverlink = 1,
-    exports = [":gradle-api-3.2"],
-    visibility = ["//visibility:public"],
-)