Add kotlin-stdlib-jdk8 when using Kotlin

kotlin-stdlib-jdk8 contains extensions to the Kotlin standard library
for use when targeting Java language level 8.

Test: m checkbuild
Change-Id: Iac5f977f9080d8e0e2402b08a992a93c909744e9
diff --git a/java/java.go b/java/java.go
index 866b33c..3fa8500 100644
--- a/java/java.go
+++ b/java/java.go
@@ -517,7 +517,8 @@
 	if j.hasSrcExt(".kt") {
 		// TODO(ccross): move this to a mutator pass that can tell if generated sources contain
 		// Kotlin files
-		ctx.AddVariationDependencies(nil, kotlinStdlibTag, "kotlin-stdlib")
+		ctx.AddVariationDependencies(nil, kotlinStdlibTag,
+			"kotlin-stdlib", "kotlin-stdlib-jdk7", "kotlin-stdlib-jdk8")
 		if len(j.properties.Plugins) > 0 {
 			ctx.AddVariationDependencies(nil, kotlinAnnotationsTag, "kotlin-annotations")
 		}
@@ -793,7 +794,7 @@
 					deps.staticResourceJars = append(deps.staticResourceJars, dep.(*AndroidApp).exportPackage)
 				}
 			case kotlinStdlibTag:
-				deps.kotlinStdlib = dep.HeaderJars()
+				deps.kotlinStdlib = append(deps.kotlinStdlib, dep.HeaderJars()...)
 			case kotlinAnnotationsTag:
 				deps.kotlinAnnotations = dep.HeaderJars()
 			}