Add experimental option to use OpenJDK 11 toolchain.

With this change, setting the environment variable
EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN=true switches from the OpenJDK 9
toolchain to the OpenJDK 11 one (prebuilts/jdk/jdk11).

Since the version of the java.base module has to match the version of
the jlink tool which consumes it, the --module-version argument to the
jmod create call is also switched.

Test: make
Test: EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN make
Bug: 131683177
Change-Id: I606d22538165f309fe5537bd67a26390b1dd5771
diff --git a/ui/build/config.go b/ui/build/config.go
index def3345..919b9ce 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -214,10 +214,14 @@
 	// Configure Java-related variables, including adding it to $PATH
 	java8Home := filepath.Join("prebuilts/jdk/jdk8", ret.HostPrebuiltTag())
 	java9Home := filepath.Join("prebuilts/jdk/jdk9", ret.HostPrebuiltTag())
+	java11Home := filepath.Join("prebuilts/jdk/jdk11", ret.HostPrebuiltTag())
 	javaHome := func() string {
 		if override, ok := ret.environ.Get("OVERRIDE_ANDROID_JAVA_HOME"); ok {
 			return override
 		}
+		if toolchain11, ok := ret.environ.Get("EXPERIMENTAL_USE_OPENJDK11_TOOLCHAIN"); ok && toolchain11 == "true" {
+			return java11Home
+		}
 		return java9Home
 	}()
 	absJavaHome := absPath(ctx, javaHome)
@@ -228,11 +232,13 @@
 	if path, ok := ret.environ.Get("PATH"); ok && path != "" {
 		newPath = append(newPath, path)
 	}
+
 	ret.environ.Unset("OVERRIDE_ANDROID_JAVA_HOME")
 	ret.environ.Set("JAVA_HOME", absJavaHome)
 	ret.environ.Set("ANDROID_JAVA_HOME", javaHome)
 	ret.environ.Set("ANDROID_JAVA8_HOME", java8Home)
 	ret.environ.Set("ANDROID_JAVA9_HOME", java9Home)
+	ret.environ.Set("ANDROID_JAVA11_HOME", java11Home)
 	ret.environ.Set("PATH", strings.Join(newPath, string(filepath.ListSeparator)))
 
 	outDir := ret.OutDir()