[8u] 8062808: Turn on the -Wreturn-type warning

[Liu, Xin]

Hi,


I'd like to backport JDK-8062808.  Enabling -Wreturn-type helps us to catch undefined code.  Could you review it and update label in that issue?

webrev: https://cr.openjdk.java.net/~xliu/8062808/webrev/


It's almost a clean patch. One single difference is that original patch doesn't include perfData.hpp. It has been changed in JDK-8064811. When we backported JDK-8064811 to jdk8u, I think we drop it by mistake.


I have verified it using the jdk8u repo. Both fastdebug and slowdebug work as expected.


thanks,

--lx