[ASan] [SystemZ] Mark segv_read_write.c as UNSUPPORTED.

[• koriakin]

Summary

On s390*-linux, sigcontext just doesn't contain any information that could
be used to recover the type of access, so there's no way to fix this, short
of emulating the faulting instruction.

compiler-rt/trunk/test/asan/TestCases/Linux/segv_read_write.c

 // RUN: %clangxx_asan -std=c++11 -O0 %s -o %t
 // RUN: not %run %t       2>&1 | FileCheck %s --check-prefix=READ
 // RUN: not %run %t write 2>&1 | FileCheck %s --check-prefix=WRITE
-// UNSUPPORTED: powerpc64,mips
+// UNSUPPORTED: powerpc64,mips,s390
 
 #include <sys/mman.h>
 
 static volatile int sink;
 __attribute__((noinline)) void Read(int *ptr) { sink = *ptr; }
 __attribute__((noinline)) void Write(int *ptr) { *ptr = 0; }
 int main(int argc, char **argv) {
   // Writes to shadow are detected as reads from shadow gap (because of how the