Investigate 128bit integers on 32bit platforms

From this issue https://github.com/antoyo/rustc_codegen_gcc/issues/71 it seems there may be issues for 128bit integers on 32bit platforms with GCC. We have some test cases using them such as: https://github.com/Rust-GCC/gccrs/blob/master/gcc/testsuite/rust/compile/torture/primconsts.rs

Which are being run on a build farm which includes 32-bit platforms: https://builder.wildebeest.org/buildbot/#/ though this is not a thorough enough test for 128bit integers but it does seem to compile at least.

And the check for the integer not supported seems to be a front-end error in c/c-decl.c as shown from this issue: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60846 but not sure what the code being generated actually looks like for 32bit platforms with that test case.

c/c-decl.c                                                                                                                 
11247:                      "%<__int%d%> is not supported on this target",     
11459:                      "%<_Float%d%s%> is not supported on this target",

Start with gcc/testsuite/rust/compile/torture/primconsts.rs and compare its results on the 32-bit build-farm targets. Read the cited c/c-decl.c diagnostics and inspect the generated code or compiler behavior for 128-bit integers. Done means determining whether 32-bit support is incorrect or already working, with reproducible findings and any needed regression coverage identified.