[compiler-rt][SystemZ] Skip fuzzer/coverage.test

This test is currently marked as XFAIL on s390x, but it is randomly
passing, causing build bot issues.  Setting as UNSUPPORTED for now.

Author: uweigand

compiler-rt/test/fuzzer/coverage.test

@@ -1,7 +1,7 @@
 # FIXME: Disabled on Windows because -fPIC cannot be used to compile for Windows.
 UNSUPPORTED: windows
 # FIXME: CreatePCArray() emits PLT stub addresses for entry blocks, which are ignored by TracePC::PrintCoverage().
-XFAIL: s390x
+UNSUPPORTED: s390x
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable  %S/NullDerefTest.cpp -o %t-NullDerefTest
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO1.cpp -fPIC %ld_flags_rpath_so1 -O0 -shared -o %dynamiclib1
 RUN: %cpp_compiler -mllvm -use-unknown-locations=Disable %S/DSO2.cpp -fPIC %ld_flags_rpath_so2 -O0 -shared -o %dynamiclib2