Add comments regarding isPIEDefault usage for r207520

Differential Revision: http://reviews.llvm.org/D2668

llvm-svn: 207521
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index bda4edf..3695166 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -6920,6 +6920,8 @@
     !Args.hasArg(options::OPT_static) &&
     (Args.hasArg(options::OPT_pie) || ToolChain.isPIEDefault() ||
      // On Android every code is PIC so every executable is PIE
+     // Cannot use isPIEDefault here since otherwise
+     // PIE only logic will be enabled during compilation
      isAndroid);
 
   ArgStringList CmdArgs;