[XRay][compiler-rt] Add a test for -fPIE

[dberris]

Summary

Ensure that builds using -fPIE and -mpie-copy-relocations and XRay work
just fine.

[dberris]

@pelikan points out offline that this isn't exactly exercising quite the right parts of clang that will make copy relocations. I'll stew on this a little and try to figure out a way to make sure we're doing the right thing here.

[dberris]

Realized that this isn't the best way to approach this (and that it's not something we actually need to test this way). Closing for further exploration later.

test/xray/TestCases/Linux/pie_test.cc

+// Test to ensure if we handle PIE executables properly.
+
+// RUN: %clangxx_xray -fxray-instrument -std=c++11 -fPIE %s -o %t
+// RUN: XRAY_OPTIONS="patch_premain=true verbosity=1 xray_logfile_base=pie-test-logging-" %run %t 2>&1 | FileCheck %s
+//
+// RUN: %clangxx_xray -fxray-instrument -std=c++11 -fPIE -mpie-copy-relocations %s -o %t
+// RUN: XRAY_OPTIONS="patch_premain=true verbosity=1 xray_logfile_base=pie-test-logging-" %run %t 2>&1 | FileCheck %s
+// RUN: rm pie-test-logging-*
+
+#include <cstdio>
+
+[[clang::xray_always_instrument]]
+unsigned short foo (unsigned b);
+
+[[clang::xray_always_instrument]]
+unsigned short bar (unsigned short a)
+{
+  printf("bar() is always instrumented!\n");
+  return foo(a);
+}
+
+unsigned short foo (unsigned b)
+{
+  printf("foo() is always instrumented!\n");
+  return b + b + 5;
+}
+
+int main ()
+{
+  // CHECK: XRay: Log file in 'pie-test-logging-{{.*}}'
+  bar(10);
+  // CHECK: bar() is always instrumented!
+  // CHECK-NEXT: foo() is always instrumented!
+}