Rename `is32bit` with a more precise name about dmtcp

[gc00]

@karya0: Really good point.
What about isM32 or isMultiarch32?

For inspiration, I started looking at https://wiki.debian.org/Multiarch and: https://wiki.debian.org/Multiarch/LibraryPathOverview .

I found this paragraph:
To solve this problem, the GCC back-end may provide a secondary OS
multilib suffix which is used in place of the primary multilib suffix
for all library directories derived from system paths as opposed to
GCC paths. For example, in the typical bi-arch setup, the -m32 option is associated with the OS multilib suffix "../lib". Given the that primary
system library directory is /usr/lib64 on such systems, this has the
effect of causing the toolchain to search ...

[gc00]

Still thinking about the right name. What about is32bitElfIn64bitOS?

[gc00]

Also, a better design would be to set is32bitElf (or the new name) always to false when we're in a 32-bit Linux O/S. After pull request #97 (to fix a bug in 32-bit Linux), let's do a later pull request with this fix.
    (It's better to get DMTCP working correctly first, and then do polishing of the code in a later commit.)