RFR (XS) 8076236: VM permits illegal flags for class init method

[harold seigel]

Hi,

Please review this small fix for JDK-8076236.  The fix moves the check 
for multiple access flags so that it covers all methods in a class 
including instance initialization methods.

Open webrev:  http://cr.openjdk.java.net/~hseigel/bug_8076236/

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8076236

The fix was tested with the JCK lang, vm, and api tests, hotspot jtreg 
tests, testbase split_verifier and quick tests, and the test cases 
provided in the bug.  No new tests are included with this fix because 
new JCK tests will test this.

Thanks, Harold