RFR: 8062672: JVM crashes during GC on various asserts which checks that HeapWord ptr is an oop

[Stefan Johansson]

Hi,

Please review this fix for the linux-sparc issue described in:
https://bugs.openjdk.java.net/browse/JDK-8062672

Webrev:
http://cr.openjdk.java.net/~sjohanss/8062672/hotspot.00/

Summary:
This fix is based on 7u-dev because the most linux-sparc testing is done 
for that release and also because it's unclear if we have time to move 
the fix the normal way through 9 and 8u before going into 7u. But the 
main reason is that it would be good to get testing of the fix in 7u 
before porting it to 8u and 9.

The fix it self is fairly simple, after JDK-8029190 was backported the 
condition for disabling UseMemSetInBOT changed from is_niagara() to 
has_blk_init(). This worked well for solaris-sparc but on linux-sparc we 
previously only set the niagara feature bits, so this change adds 
support for detecting blk_init support on linux-sparc.

Testing:
Crashes/asserts was reproducible without the fix and after the fix none 
have been observed. Also verified that UseMemSetInBOT now is set to 
false as it should be.

Thanks,
Stefan