8204152: SignedObject throws NullPointerException for null keys with an initialized Signature object Summary: Check for null and throw InvalidKeyException to maintain same behavior Reviewed-by: xuelei

8203680: os::stat() on Posix platform does not need to copy input path Reviewed-by: hseigel, dholmes

8153107: enabling ObjectSynchronizer::quick_enter() on ARM64 causes hangs Summary: Always set the markword for recursive monitors in MacroAssembler::fast_lock(). Reviewed-by: aph, drwhite, dcubed, bulasevich