(11) RFR (S) JDK-8197864: VS2017 (C4334) Result of 32-bit Shift Implicitly Converted to 64 bits

[Lois Foltan]

Please review this fix to properly perform a 64-bit shift when setting 
SlowSignatureHandler::_fp_identifiers within _WIN64 conditional code.  
Since the compiler determined that the constant could fit into an int 
and the type of SlowSignatureHandler::_num_args is of unsigned int as 
well, a 32-bit shift would result yielding a VS2017 compilation warning.

open webrev at http://cr.openjdk.java.net/~lfoltan/bug_jdk8197864/webrev/
bug link https://bugs.openjdk.java.net/browse/JDK-8197864
contributed-by: Kim Barrett & Lois Foltan

Testing: hs-tier(1-3), jdk-tier(1-3) complete

Thanks,
Lois