[TSan] Provide default values for compile definitions.

Provide defaults for TSAN_COLLECT_STATS and TSAN_NO_HISTORY.
Replace #ifdef directives with #if. This fixes a bug introduced
in r229112, where building TSan runtime with -DTSAN_COLLECT_STATS=0
would still enable stats collection and reporting.

llvm-svn: 229581
diff --git a/compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cc b/compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cc
index 3ca9793..8ed1fbf 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cc
+++ b/compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cc
@@ -145,7 +145,7 @@
   AllocatorThreadFinish(thr);
 #endif
   thr->~ThreadState();
-#ifdef TSAN_COLLECT_STATS
+#if TSAN_COLLECT_STATS
   StatAggregate(ctx->stat, thr->stat);
 #endif
   thr = 0;