[clang-format] Align block comment decorations

Summary:
This patch implements block comment decoration alignment.

source:
```
/* line 1
* line 2
*/
```

result before:
```
/* line 1
* line 2
*/
```

result after:
```
/* line 1
 * line 2
 */
```

Reviewers: djasper, bkramer, klimek

Reviewed By: klimek

Subscribers: mprobst, cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D29943

llvm-svn: 295312
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index 72fd0df..7497cab 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1966,7 +1966,7 @@
       format("#define A \\\nint i;\\\n  int j;", getLLVMStyleWithColumns(11)));
   EXPECT_EQ("#define A\n\nint i;", format("#define A \\\n\n int i;"));
   EXPECT_EQ("template <class T> f();", format("\\\ntemplate <class T> f();"));
-  EXPECT_EQ("/* \\  \\  \\\n*/", format("\\\n/* \\  \\  \\\n*/"));
+  EXPECT_EQ("/* \\  \\  \\\n */", format("\\\n/* \\  \\  \\\n */"));
   EXPECT_EQ("<a\n\\\\\n>", format("<a\n\\\\\n>"));
 }