[compiler-rt][test] XFAIL two tests on 32-bit sparc

Two tests `FAIL` on 32-bit sparc:

  Profile-sparc :: Posix/instrprof-gcov-parallel.test
  UBSan-Standalone-sparc :: TestCases/Float/cast-overflow.cpp

The failure mode is similar:

  Undefined                       first referenced
   symbol                             in file
  __atomic_store_4                    /var/tmp/instrprof-gcov-parallel-6afe8d.o
  __atomic_load_4                     /var/tmp/instrprof-gcov-parallel-6afe8d.o

  Undefined                       first referenced
   symbol                             in file
  __atomic_load_1                     /var/tmp/cast-overflow-72a808.o

This is a known bug: `clang` doesn't inline atomics on 32-bit sparc, unlike
`gcc`.

The patch therefore `XFAIL`s the tests.

Tested on `sparcv9-sun-solaris2.11` and `amd64-pc-solaris2.11`.

Differential Revision: https://reviews.llvm.org/D85346