Revert "[openmp] [test] XFAIL many-microtask-args.c on ARM"

This reverts commit 03bf001b.

This commit broke a number of OpenMP buildbots, e.g.
https://lab.llvm.org/buildbot#builders/84/builds/31839, where
the build ends up with errors like this:

[0/1] Running OpenMP tests
llvm-lit: /b/1/openmp-clang-x86_64-linux-debian/llvm.src/llvm/utils/lit/lit/TestingConfig.py:140: fatal: unable to parse config file '/b/1/openmp-clang-x86_64-linux-debian/llvm.build/projects/openmp/libomptarget/test/x86_64-pc-linux-gnu/lit.site.cfg', traceback: Traceback (most recent call last):
 File "/b/1/openmp-clang-x86_64-linux-debian/llvm.src/llvm/utils/lit/lit/TestingConfig.py", line 129, in load_from_path
   exec(compile(data, path, 'exec'), cfg_globals, None)
 File "/b/1/openmp-clang-x86_64-linux-debian/llvm.build/projects/openmp/libomptarget/test/x86_64-pc-linux-gnu/lit.site.cfg", line 6
   config.test_compiler_features =
                                   ^
SyntaxError: invalid syntax