Fix gmp build for 32bit ubuntu.

Need to set ABI=32 when calling ./configure.
Add additional BigInt constructors for [u]int(64) args (where c_[u]long is expected).

A few tests in modules/standard/gmp were failing on linux32 to resolve calls
like "BigInt(bool, uint(64)" or "BigInt(int(64))". The intended constructors
were "BigInt(init2:bool, nbits:c_ulong)" and "BigInt(num:c_long)" respectively.

Create the [u]int(64) versions and cast from [u]int(64) to c_[u]long.
Get rid of c_[u]long BigInt constructors.

On 64bit platforms, they confuse function resolution as [u]int(64) and c_[u]long literals are the same.
Revert "Get rid of c_[u]long BigInt constructors."

This reverts commit d2883092b4be1fa14e21ee17461801d6b79c535a.
Revert "Add additional BigInt constructors for [u]int(64) args (where c_[u]long is expected)."

This reverts commit a87aca1209179319c83990de9654b2c73141548b.
Merge pull request #800 from thomasvandoren/fix-gmp-for-32bit-ubuntu

Fix gmp build for 32bit ubuntu.

Need to set ABI=32 when calling ./configure, at least for 32bit Ubuntu 14.04 desktop.

Without this setting, the configure step reports this error:

```
checking size of mp_limb_t... 4
configure: error: Oops, mp_limb_t is 32 bits, but the assembler code
in this configuration expects 64 bits.
You appear to have set $CFLAGS, perhaps you also need to tell GMP the
intended ABI, see "ABI and ISA" in the manual.
make: *** [gmp-config] Error 1
```
Lower stack size for callStackSize test

This test is intended to show that the runtime changes stack size based off of
CHPL_RT_CALL_STACK_SIZE. It used to set the value to a little over 12MB.
However on cygwin our default and max stack size are 2MB so this just lowers
the value set to a little under 1MB. It doesn't really matter what the value is
so long as it's different than the default, and it's lower than the max across
different configurations.
Use uint(64) instead of c_ulong in BigInt pidigits versions.
Merge pull request #812 from thomasvandoren/update-pidigits-types

Use uint(64) instead of c_ulong in BigInt pidigits versions.
Merge pull request #811 from ronawho/update-callStackSize-for-cygwin

Lower stack size for callStackSize test

[ok'd by @bradcray]

This test is intended to show that the runtime changes stack size based off of
CHPL_RT_CALL_STACK_SIZE. It used to set the value to a little over 12MB.
However on cygwin our default and max stack size are 2MB so this just lowers
the value set to a little under 1MB. It doesn't really matter what the value is
so long as it's different than the default, and it's lower than the max across
different configurations.