Fix 64-bit platform detection for pre C++11 compilers.

In version 3.6.3, Ice started detecting 64 bit platforms by
checking WORDSIZE. When using C++98/03, STDC_LIMIT_MACROS isn't
set by default and WORDSIZE is always set to 32, even if the
required headers weren't included beforehand. Until a proper
fix is available in base (e.g. not setting WORDSIZE at all if
STDC_LIMIT_MACROS isn't defined), we detect if C++11 or newer
is used and only rely on WORDSIZE in this case, otherwise
we fall back to detecting the platform using other macros.

PR: 216609
Reported by: jbeich