RFR: 8203220: Introduce ATTRIBUTE_ALIGNED macro

[Per Liden]

This patch introduces a global ATTRIBUTE_ALIGNED(x) macro, which expands 
to __attribute__((aligned(x)) or the equivalent of that.

We already use this attribute is some parts of the code, but we haven't 
had a macro in globalDefinitions.hpp for this.

In the src/hotspot/cpu/x86/macroAssembler_x86_*.cpp files I chose to 
keep the ALIGNED_(x) and just define it as ATTRIBUTE_ALIGNED(x), instead 
of changing all uses of it.

Also, for GCC I've included a workaround for a known bug (see the 
comment in the file). I thought it would be nice to include that since 
it might otherwise affect quite a few systems.

And finally, we don't really have a uniform naming standard for these 
types of attributes. E.g. we have NOINLINE/ALWAYSINLINE and we have 
ATTRIBUTE_PRINTF. I chose to use the ATTRIBUTE_ prefix, instead of just 
ALIGNED, since ALIGNED is somewhat generic and we already have at least 
one place where a variable is named ALIGNED, so it would conflict.

Bug: https://bugs.openjdk.java.net/browse/JDK-8203220
Webrev: http://cr.openjdk.java.net/~pliden/8203220/webrev.0

Testing: hs-tier{1,2}

/Per