x86_64: Unify 64-bit check in x86 compiler

Update x86-specific Gen64Bit() check with the CompilationUnit target64 field
which is set using unified Is64BitInstructionSet(InstructionSet) check.

Change-Id: Ic00ac863ed19e4543d7ea878d6c6c76d0bd85ce8
Signed-off-by: Elena Sayapina <elena.v.sayapina@intel.com>
9 files changed