[XRay] Make Test Work with Internal Shell

There was one test that set an environment variable without using env
and also used a subshell. These are features the internal shell does not
support. Rewrite the test to use readfile/env.

Reviewers: fmayer, MaskRay

Reviewed By: fmayer

Pull Request: llvm#165143

Author: boomanaiden154

compiler-rt/test/xray/TestCases/Posix/fdr-single-thread.cpp

@@ -1,11 +1,12 @@
 // RUN: %clangxx_xray -g -std=c++11 %s -o %t
 // RUN: rm -f fdr-logging-1thr-*
-// RUN: XRAY_OPTIONS=XRAY_OPTIONS="verbosity=1 patch_premain=true \
+// RUN: env XRAY_OPTIONS=XRAY_OPTIONS="verbosity=1 patch_premain=true \
 // RUN:   xray_fdr_log=true \
 // RUN:   xray_fdr_log_func_duration_threshold_us=0 \
 // RUN:   xray_logfile_base=fdr-logging-1thr-" %run %t 2>&1
+// RUN: ls fdr-logging-1thr-* | head -n1 | tr -d '\n' > %t.xray_input
 // RUN: %llvm_xray convert --output-format=yaml --symbolize --instr_map=%t \
-// RUN:   "`ls fdr-logging-1thr-* | head -n1`" | FileCheck %s
+// RUN:   "%{readfile:%t.xray_input}" | FileCheck %s
 // RUN: rm fdr-logging-1thr-*
 
 // UNSUPPORTED: target=arm{{.*}}