Suppress exportString tests that fail with CHPL_TARGET_COMPILER=cray-prgenv-cray

[dlongnecke-cray]

This PR suppresses two tests that currently fail in a cray-xc environment with CHPL_TARGET_COMPILER=cray-prgenv-cray. The Chapel type c_ptr(c_char) currently maps to int8_t* on most systems, which causes the GNU compiler to emit warnings that can be suppressed with -Wno-pointer-sign. There is no equivalent for Cray CC, so we should suppress these tests until #6041 is resolved.

[dlongnecke-cray]

@gbtitus, I am unsure of how to replicate the testing environment listed below:

    CHPL_HOST_PLATFORM: cray-xc
    CHPL_HOST_COMPILER: gnu
    CHPL_HOST_ARCH: x86_64
    CHPL_TARGET_PLATFORM: cray-xc *
    CHPL_TARGET_COMPILER: cray-prgenv-cray
    CHPL_TARGET_ARCH: x86_64
    CHPL_TARGET_CPU: ivybridge
    CHPL_LOCALE_MODEL: flat
    CHPL_COMM: none *
    CHPL_TASKS: qthreads
    CHPL_LAUNCHER: none *
    CHPL_TIMERS: generic
    CHPL_UNWIND: none
    CHPL_MEM: jemalloc
    CHPL_ATOMICS: intrinsics
    CHPL_GMP: system
    CHPL_HWLOC: hwloc
    CHPL_REGEXP: re2
    CHPL_LLVM: none
    CHPL_AUX_FILESYS: none
    CHPL_LIB_PIC: none

When I run the tests in test/interop/C/exportString the C tests are skipped. Additionally my $(CC) compiler is clang-9. Is there some module loading/unloading I have to do to match the nightly testing environment, here? (I suspect there is, and will look into it, just a prelude question if you will).

[gbtitus]

@gbtitus, I am unsure of how to replicate the testing environment listed below:

Yes, you'll have to do some module adjustment to replicate this environment. Generally: on the system where the corresponding testing is done, make sure the PrgEnv module you have loaded is PrgEnv-cray. That selects the target compiler. You'll also need to export CHPL_COMM=none explicitly, because the default comm layer on XC systems is ugni. And you'll need to export CHPL_LAUNCHER=none explicitly, because the default launcher on XC systems is whatever (PBS or slurm) is installed on the system.

[gbtitus]

Modulo the slight phrasing change I mentioned this looks good, but I'd like to see it tested before merging.

[dlongnecke-cray]

Thank you for the help!