build: llvmInstallPath becomes /opt/local/libexec/llvm-3.8

NOTE: if for some reasons you need to redefine this values,
please add it to local.property

build.gradle

@@ -1,5 +1,7 @@
 ant.importBuild 'backend.native/kotlin-ir/build.xml'
 
-Properties props = new Properties()
-props.load(new FileInputStream("$project.rootDir/local.properties"))
-props.each {prop -> project.ext.set(prop.key, prop.value)}
+if (new File("$project.rootDir/local.properties").exists()) {
+  Properties props = new Properties()
+  props.load(new FileInputStream("$project.rootDir/local.properties"))
+  props.each {prop -> project.ext.set(prop.key, prop.value)}
+}

gradle.properties

@@ -1 +1,2 @@
 kotlin_version=1.0.4
+llvmInstallPath=/opt/local/libexec/llvm-3.8