Motivated by a surprise of a colleague that with -m32,
no offload dumps were created; that's because mkoffload
does not process host binaries when the are 32bit (i.e. ilp32).

Internally, that done as follows: The host compiler passes to
'mkoffload' the used host ABI, i.e. -foffload-abi=ilp32 or -foffload-abi=lp64

That's done via TARGET_OFFLOAD_OPTIONS, which is supported by aarch64, i386, and rs6000.

While it is sensible (albeit not strictly required) that GCC requires that
the host and device side agree and that only 64bit is implemented for the
device side, it can be confusing that silently no offloading code is generated.


Hence, I propose to print a warning in that case - as implemented in the attached patch:

$ gcc -fopenmp -m32 test.c
nvptx mkoffload: warning: offload code generation skipped: offloading with 32-bit host code is currently not supported
gcn mkoffload: warning: offload code generation skipped: offloading with 32-bit host code is currently not supported

* * *

This shouldn't have any effect on offload builds using -m64
and non-offload builds – while several testcases already have
issues with '-m32' when offloading is enabled or an offloading
device is available.

To make it not worse, this patch adds some pruning and for
a subset of the failing testcases, I added code to avoids FAILS.
There are some more fails, but those aren't new.

Comments, remarks, suggestions?
Is the mkoffload.cc part is okay?

Tobias