Generate Java 8 bytecode with Kotlin compiler

This commit also updates Kotlin from beta 2 to RC.

Issue: SPR-15183

build.gradle

@@ -6,7 +6,7 @@ buildscript {
 	dependencies {
 		classpath("io.spring.gradle:propdeps-plugin:0.0.8")
 		classpath("org.asciidoctor:asciidoctor-gradle-plugin:1.5.3")
-		classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.1.0-beta-38")
+		classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.1.0-rc-91")
 		classpath("io.spring.gradle:docbook-reference-plugin:0.3.1")
 		classpath("io.spring.gradle:dependency-management-plugin:1.0.0.BUILD-SNAPSHOT")
 	}
@@ -71,7 +71,7 @@ configure(allprojects) { project ->
 	ext.junitVersion           = "4.12"
 	ext.junitJupiterVersion    = '5.0.0-M3'
 	ext.junitPlatformVersion   = '1.0.0-M3'
-	ext.kotlinVersion          = "1.1.0-beta-38"  // also change kotlin-gradle-plugin version when upgrading
+	ext.kotlinVersion          = "1.1.0-rc-91"  // also change kotlin-gradle-plugin version when upgrading
 	ext.log4jVersion           = '2.8'
 	ext.nettyVersion           = "4.1.8.Final"
 	ext.okhttpVersion          = "2.7.5"
@@ -110,6 +110,12 @@ configure(allprojects) { project ->
 	// Kotlin compiler does not support JDK 9 yet, see https://youtrack.jetbrains.com/issue/KT-14988
 	if (!JavaVersion.current().java9Compatible) {
 		apply plugin: "kotlin"
+		compileKotlin {
+			kotlinOptions.jvmTarget = "1.8"
+		}
+		compileTestKotlin {
+			kotlinOptions.jvmTarget = "1.8"
+		}
 	}
 
 	configurations {
@@ -403,7 +409,7 @@ project("spring-core") {
 		optional("net.sf.jopt-simple:jopt-simple:5.0.3")
 		optional("org.aspectj:aspectjweaver:${aspectjVersion}")
 		optional("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		optional("org.reactivestreams:reactive-streams")
 		optional("io.projectreactor:reactor-core")
 		optional "io.reactivex:rxjava:${rxjavaVersion}"
@@ -441,7 +447,7 @@ project("spring-beans") {
 		compile(files(project(":spring-core").cglibRepackJar))
 		optional("javax.inject:javax.inject:1")
 		optional("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		optional("org.yaml:snakeyaml:${snakeyamlVersion}")
 		testCompile("org.apache.tomcat.embed:tomcat-embed-core:${tomcatVersion}")
 	}
@@ -536,7 +542,7 @@ project("spring-context") {
 		optional("org.aspectj:aspectjweaver:${aspectjVersion}")
 		optional("org.codehaus.groovy:groovy-all:${groovyVersion}")
 		optional("org.beanshell:bsh:2.0b5")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		testCompile("org.apache.commons:commons-pool2:2.4.2")
 		testCompile("org.slf4j:slf4j-api:${slf4jVersion}")
 		testCompile("javax.inject:javax.inject-tck:1")
@@ -614,7 +620,7 @@ project("spring-messaging") {
 		testCompile("org.xmlunit:xmlunit-matchers:${xmlunitVersion}")
 		testCompile("org.slf4j:slf4j-jcl:${slf4jVersion}")
 		testCompile("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
-		testCompile("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		testCompile("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		testRuntime("javax.activation:activation:${activationApiVersion}")
 		testRuntime("com.sun.xml.bind:jaxb-core:${jaxbVersion}")
 		testRuntime("com.sun.xml.bind:jaxb-impl:${jaxbVersion}")
@@ -678,7 +684,7 @@ project("spring-jdbc") {
 		optional("org.apache.derby:derby:10.13.1.1")
 		optional("org.apache.derby:derbyclient:10.13.1.1")
 		optional("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 	}
 }
 
@@ -780,7 +786,7 @@ project("spring-web") {
 		optional("javax.xml.bind:jaxb-api:${jaxbVersion}")
 		optional("javax.xml.ws:jaxws-api:${jaxwsVersion}")
 		optional("javax.mail:javax.mail-api:${javamailVersion}")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		testCompile(project(":spring-context-support"))  // for JafMediaTypeFactory
 		testCompile("io.projectreactor.addons:reactor-test")
 		testCompile("org.apache.taglibs:taglibs-standard-jstlel:1.2.1") {
@@ -843,7 +849,7 @@ project("spring-webflux") {
 			exclude group: "org.jboss.spec.javax.websocket", module: "jboss-websocket-api_1.1_spec"
 		}
 		optional("org.jetbrains.kotlin:kotlin-reflect:${kotlinVersion}")
-		optional("org.jetbrains.kotlin:kotlin-stdlib:${kotlinVersion}")
+		optional("org.jetbrains.kotlin:kotlin-stdlib-jre8:${kotlinVersion}")
 		testCompile("io.projectreactor.addons:reactor-test")
 		testCompile("javax.validation:validation-api:${beanvalVersion}")
 		testCompile("org.hibernate:hibernate-validator:${hibval5Version}")