Changes

Introduce gcThreadsCountSpecified flag

This flag is to be used along existing gcThreadCountForced. Specified
flag will be used to distinguish between GC thread count calculated by
default or specified by a command line option. Forced flag
will to be used for a subset of options that force a fixed number of
threads.

Currently Forced is used as Specified, but we need both to distinguish
among 3 posibilities, specifically in Java: default, Xgcthreads and
Xgcmaxthreads.

Changes that will make that behavior effective will follow up later,
once downstream projects properly adjust command line parsing and
setting these flags.

Signed-off-by: Aleksandar Micic <Aleksandar_Micic@ca.ibm.com>
 (commit: d253adb)