[compiler-rt][xray] Disable fdr-reinit test on Arm

This test is still seemingly randomly segfaulting on Arm:
https://lab.llvm.org/buildbot/#/builders/178/builds/1547

Though it seems to fail earlier in the test than on AArch64.
Investigation continues.

Author: DavidSpickett

compiler-rt/test/xray/TestCases/Posix/fdr-reinit.cpp

@@ -1,5 +1,5 @@
-// This will sometimes segfault on the AArch64 bots
-// UNSUPPORTED: aarch64
+// This will sometimes segfault on the AArch64 and Arm bots
+// UNSUPPORTED: aarch64, arm
 // RUN: %clangxx_xray -g -std=c++11 %s -o %t
 // RUN: rm xray-log.fdr-reinit* || true
 // RUN: XRAY_OPTIONS="verbosity=1" %run %t