Prevent DCE on __lsan_is_turned_off and re-enable test case

Summary:
-dead_strip in ld64 strips weak interface symbols, which I believe
is most likely the cause of this test failure. Re-enable after marking the interface
function as used.

Reviewers: alekseyshl, kubamracek, kcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37635

llvm-svn: 312824

compiler-rt/include/sanitizer/lsan_interface.h

@@ -64,6 +64,8 @@ extern "C" {
   // for the program it is linked into (if the return value is non-zero). This
   // function must be defined as returning a constant value; any behavior beyond
   // that is unsupported.
+  // To avoid dead stripping, you may need to define this function with
+  // __attribute__((used))
   int __lsan_is_turned_off();
 
   // This function may be optionally provided by the user and should return

compiler-rt/test/lsan/TestCases/link_turned_off.cc

@@ -3,15 +3,13 @@
 // RUN: %clangxx_lsan %s -o %t
 // RUN: %env_lsan_opts=$LSAN_BASE %run %t
 // RUN: %env_lsan_opts=$LSAN_BASE not %run %t foo 2>&1 | FileCheck %s
-//
-// UNSUPPORTED: darwin
 
 #include <sanitizer/lsan_interface.h>
 
 int argc_copy;
 
 extern "C" {
-int __lsan_is_turned_off() {
+int __attribute__((used)) __lsan_is_turned_off() {
   return (argc_copy == 1);
 }
 }