[15] RFR (M): 8238681: Make -XX:UseSSE flag x86-specific

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8238681/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8238681

Turn UseSSE into x86-specific flag since it doesn't have any meaning on 
non-x86 platforms.

As a cleanup, I made all the code which assumes UseSSE<2 x86-32 
specific. (x86-64 ABI requires SSE2.)

Also, as a precaution, I made UseSSE obsolete on non-x86 platforms.

Testing: hs-precheckin-comp, tier1-5, linux x86-32 fastdebug build.

Thanks!

Best regards,
Vladimir Ivanov