[lsan] Change CMakeLists to build the common LSan module for ASan.
Also, define CAN_SANITIZE_LEAKS.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182383 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/lsan/lsan_common.cc b/lib/lsan/lsan_common.cc
index d9e7d81..18d913d 100644
--- a/lib/lsan/lsan_common.cc
+++ b/lib/lsan/lsan_common.cc
@@ -21,7 +21,7 @@
 #include "sanitizer_common/sanitizer_stoptheworld.h"
 
 namespace __lsan {
-
+#if CAN_SANITIZE_LEAKS
 Flags lsan_flags;
 
 static void InitializeFlags() {
@@ -381,5 +381,8 @@
            remaining > 1 ? "s" : "");
   }
 }
-
+#else  // CAN_SANITIZE_LEAKS
+void InitCommonLsan() {}
+void DoLeakCheck() {}
+#endif  // CAN_SANITIZE_LEAKS
 }  // namespace __lsan