RFR: 8200106: Move NoSafepointVerifier out from gcLocker.hpp

[Stefan Karlsson]

Hi all,

Please review this patch to separate out the NoSafepointVerifier class 
(and friends) from gcLocker.hpp into its own file.

http://cr.openjdk.java.net/~stefank/8200106/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8200106

After this patch gcLocker.hpp only contains code for the GCLocker. I've 
gone through all usages of the GCCLocker and NoSafepointVerifier classes 
and changed the code to include the correct headers.

The new files are names safepointVerifiers.hpp/cpp and the main class is 
NoSafepointVerifier. However, I also moved the NoGCVerifier, which is 
the parent class of NoSafepointVerifier, and NoAllocVerfier. I think all 
of these are used to verify that we don't do things that will interact 
badly with safepoints, hence the name of the new file. Are others OK 
with the name?

Thanks,
StefanK