Add back the leading space when printing commands with -###

This was an unintentional behavior change from r214924.

llvm-svn: 215044
diff --git a/clang/lib/Driver/Job.cpp b/clang/lib/Driver/Job.cpp
index fdf730d..7d6d0bb 100644
--- a/clang/lib/Driver/Job.cpp
+++ b/clang/lib/Driver/Job.cpp
@@ -96,6 +96,7 @@
 void Command::Print(raw_ostream &OS, const char *Terminator, bool Quote,
                     bool CrashReport) const {
   // Always quote the exe.
+  OS << ' ';
   PrintArg(OS, Executable, /*Quote=*/true);
 
   for (size_t i = 0, e = Arguments.size(); i < e; ++i) {