AIX supports both 32-bit and 64-bit environments (with 32-bit being the default). This patch improves support for building LLVM on AIX in both 32-bit and 64-bit mode.
- Change host detection to return correct 32/64-bit triple as config_guess does not return the correct version on 64-bit. This can confuse JIT tests and other things that care about what the host triple is.
- Remove manual setting of 64-bit flags on AIX. AIX provides OBJECT_MODE environment variable to enable the user to obtain a 64-bit development environment. CMake will properly set these flags provided the user sets the correct OBJECT_MODE before configuring and setting them manually will interfere with 32-bit builds.
- Don't present the LLVM_BUILD_32_BITS option on AIX, users should use OBJECT_MODE when running CMake instead.