Switch default JVM target to 1.8

#KT-29405 Fixed

compiler/testData/codegen/bytecodeText/inlineClasses/skipCallToUnderlyingValueOfInlineClass.kt

@@ -9,7 +9,7 @@ inline class UInt(val value: Int)
 fun test(u1: UInt, u2: UInt) {
     val a = u1.value
 
-    val b = u1.value.hashCode() // box int to call hashCode
+    val b = u1.value.hashCode()
     val c = u1.value + u2.value
 }
 
@@ -18,5 +18,5 @@ fun test(u1: UInt, u2: UInt) {
 // 0 INVOKESTATIC UInt\$Erased.box
 // 0 INVOKEVIRTUAL UInt.unbox
 
-// 1 valueOf
-// 0 intValue
+// 0 valueOf
+// 0 intValue