Create an absolute javabase target for testing

PiperOrigin-RevId: 211672735

tools/jdk/BUILD

diff --git a/tools/jdk/BUILD b/tools/jdk/BUILD
index a42f165..a8a13cb 100644
--- a/tools/jdk/BUILD
+++ b/tools/jdk/BUILD
@@ -19,6 +19,16 @@
 
 java_toolchain_alias(name = "current_java_toolchain")
 
+# Used to set --host_javabase or --javabase to a local JDK without having to define
+# a custom java_runtime rule.
+# E.g.:
+# bazel build --host_javabase=@bazel_tools//tools/jdk:absolute_javabase \
+#   --define=ABSOLUTE_JAVABASE=<path to JDK> ...
+java_runtime(
+    name = "absolute_javabase",
+    java_home = "$(ABSOLUTE_JAVABASE)",
+)
+
 filegroup(
     name = "BUILD-jdk",
     srcs = [":BUILD"],