[XRay][compiler-rt][NFC] Clean up xray log files before running test

Improves the test behaviour in the face of failure. Without this change
the fdr-single-thread.cc test may leave around artefacts of a previous
failing run since the cleanup doesn't happen if any of the intermediary
steps fail.

Non-functional change.

Subscribers: llvm-commits
llvm-svn: 316548

compiler-rt/test/xray/TestCases/Linux/fdr-single-thread.cc

@@ -1,4 +1,5 @@
 // RUN: %clangxx_xray -g -std=c++11 %s -o %t
+// RUN: rm fdr-logging-1thr-* || true
 // RUN: XRAY_OPTIONS=XRAY_OPTIONS="verbosity=1 patch_premain=true \
 // RUN:   xray_naive_log=false xray_fdr_log=true \
 // RUN:   xray_fdr_log_func_duration_threshold_us=0 \