Request for reviews (S): 8005522: use fast-string instructions on x86 for zeroing

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/8005522/webrev/

8005522: use fast-string instructions on x86 for zeroing

New x86 processors enhanced the operation of the REP MOVSB and REP STOSB 
instructions. Use 'rep stosb' instead of 'rep stosq' when fast-string 
operations are available (cpuid ERMS bit is set).

Ran compiler regression tests on machine which has fast-string 
operations with 64- and 32-bit VM.

Thanks,
Vladimir