RFR(S): 7147740: add assertions to check stack alignment on VM entry from generated code (x64)

[Vladimir Kozlov]

OK. Looks good.

Vladimir

Roland Westrelin wrote:
>> Why you don't check it on windows_x86?
> 
> Only because it's harder for me to build and test on windows and I assume testing on linux and solaris is sufficient to catch all problems.
> 
> Roland.