Use gradle toolchains in the buildscript

build.gradle.kts

@@ -28,6 +28,7 @@ architectury {
 }
 
 val javaVer: String = "8"
+val sourceJavaVer: String = "16"
 val kotlinVer: String by rootProject
 val kotlinBaseVer = kotlinVer.substring(0..2)
 val mcBase: String = rootProject.architectury.minecraft.substring(0..3)
@@ -152,9 +153,7 @@ allprojects {
     apply(plugin = "java")
     apply(plugin = "org.jetbrains.kotlin.jvm")
     apply(plugin = "architectury-plugin")
-    java {
-        sourceCompatibility = JavaVersion.VERSION_11
-    }
+    val compiler = javaToolchains.compilerFor { languageVersion.set(JavaLanguageVersion.of(sourceJavaVer.toInt())) }
     dependencies {
         implementation(kotlin("stdlib-jdk8", kotlinVer))
         implementation(kotlin("reflect", kotlinVer))
@@ -178,12 +177,15 @@ allprojects {
             with(options) {
                 encoding = "UTF-8"
                 isFork = true
+                release.set(javaVer.toInt())
+                javaCompiler.set(compiler)
                 // The following lines are required for Jabel:
+                sourceCompatibility = sourceJavaVer
                 forkOptions.jvmArgs!!.addAll(listOf(
                     "--add-opens=jdk.compiler/com.sun.tools.javac.code=ALL-UNNAMED",
                     "--add-opens=jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED"
                 )) // Java 16+ support
-                compilerArgs.addAll(listOf("-Xplugin:jabel", "--release", javaVer))
+                compilerArgs.addAll(listOf("-Xplugin:jabel"))
             }
         }
         withType(ProcessResources::class) {