Temporarily restore the JDK 8 host_javabase-compatible toolchain

Unlike previously, this is not magically selected when running on JDK 8.
Use --java_toolchain=@bazel_tools//tools/jdk:toolchain_hostjdk8
--host_java_toolchain=@bazel_tools//tools/jdk:toolchain_hostjdk8 to configure
the JDK 8 host_javabase-compatible toolchain.
PiperOrigin-RevId: 207738992

tools/jdk/BUILD

diff --git a/tools/jdk/BUILD b/tools/jdk/BUILD
index 454d674..8ed37de 100644
--- a/tools/jdk/BUILD
+++ b/tools/jdk/BUILD
@@ -193,6 +193,16 @@
 )
 
 default_java_toolchain(
+    name = "toolchain_hostjdk8",
+    bootclasspath = [":platformclasspath"],
+    jvm_opts = [
+        "-Xbootclasspath/p:$(location @bazel_tools//third_party/java/jdk/langtools:javac_jar)",
+    ],
+    source_version = "8",
+    target_version = "8",
+)
+
+default_java_toolchain(
     name = "toolchain",
     bootclasspath = [":bootclasspath"],
     extclasspath = [":extclasspath"],