Move module-info.java to a java9-specific dir due to IDEA highlighting issues

Author: lion7

buildSrc/src/main/kotlin/Java9Modularity.kt

@@ -33,8 +33,10 @@ object Java9Modularity {
 
         val compileJavaModuleInfo = tasks.register("compileJavaModuleInfo", JavaCompile::class.java) {
             val moduleName = project.name.replace('-', '.') // this module's name
-            val sourceFile = compilation.defaultSourceSet.kotlin.singleOrNull { it.name == "module-info.java" }
-                ?: throw IllegalStateException("module-info.java not found in $project")
+            val sourceFile = file("${target.name.ifEmpty { "." }}/java9/module-info.java")
+            if (!sourceFile.exists()) {
+                throw IllegalStateException("$sourceFile not found in $project")
+            }
             val compileKotlinTask = compilation.compileKotlinTask as org.jetbrains.kotlin.gradle.tasks.KotlinCompile
             val targetDir = compileKotlinTask.destinationDirectory.dir("../java9")