[compiler-rt][profile] Disable oneline-merging-windows.c on Windows on Arm

This test has been failing since https://lab.llvm.org/buildbot/#/builders/161/builds/2899,
but no change in that build caused it.

I think this has always failed but llvm/llvm-zorg#252
only recently enabled in on the bot.

Author: DavidSpickett

compiler-rt/test/profile/ContinuousSyncMode/online-merging-windows.c

@@ -1,6 +1,9 @@
 // REQUIRES: target={{.*windows-msvc.*}}
 // REQUIRES: lld-available
 
+// Fails on Windows on Arm for unknown reasons.
+// UNSUPPORTED: target=aarch64-pc-windows-msvc
+
 // Test the online merging mode (%m) along with continuous mode (%c).
 //
 // Split files & cd into a temporary directory.