RFR (S): 8218939: vm/mlvm/anonloader/stress/byteMutation crashed on windows

[David Holmes]

webrev: http://cr.openjdk.java.net/~dholmes/8218939/webrev
bug: https://bugs.openjdk.java.net/browse/JDK-8218939

The bytes() in a Symbol are UTF8 but do not form a NUL-terminated 
C-string. In a couple of places in the classfile parser we are treating 
it as NUL-terminated:

- in name validation we were calling strchr to find the semi-colon, but 
this could run off through memory if there was no semi-colon (as per the 
testcase). This is replaced with memchr which takes the expected length.

- in formatting the exception message we used %s but instead we need 
%.*s and pass the length

There's a minor change to a test to print the exception information as 
that exposes the fact we were doing things incorrectly e.g:

java.lang.ClassFormatError: Illegal class name 
"p1//BadInterface1\u00f1\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00ab\u00abU" 
in class file

versus (after bug fix)

java.lang.ClassFormatError: Illegal class name "p1//BadInterface1" in 
class file UseBadInterface1

Testing:
  - re-ran failing test on Windows with seeds known to have caused failures
  - ran ran failing test on Windows 150 times with random seeds
  - tiers 1-3

Thanks,
David
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