clang-format: Don't merge lines with comments.

Before:
  int f() { // comment return 42; }

After:
  int f() { // comment
    return 42;
  }

This fixes llvm.org/PR21769.

llvm-svn: 223609
diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index cf8e5d3..ebd1290 100644
--- a/clang/lib/Format/Format.cpp
+++ b/clang/lib/Format/Format.cpp
@@ -665,6 +665,9 @@
     }
     if (I[1]->First->is(TT_FunctionLBrace) &&
         Style.BreakBeforeBraces != FormatStyle::BS_Attach) {
+      if (I[1]->Last->is(TT_LineComment))
+        return 0;
+
       // Check for Limit <= 2 to account for the " {".
       if (Limit <= 2 || (Style.ColumnLimit == 0 && containsMustBreak(TheLine)))
         return 0;