Add option to change preprocessor -CC to -C

See #37.

src/libclang/libclang_parser.cpp

@@ -48,6 +48,12 @@ bool detail::libclang_compile_config_access::fast_preprocessing(
     return config.fast_preprocessing_;
 }
 
+bool detail::libclang_compile_config_access::remove_comments_in_macro(
+    const libclang_compile_config& config)
+{
+    return config.remove_comments_in_macro_;
+}
+
 libclang_compilation_database::libclang_compilation_database(const std::string& build_directory)
 {
     static_assert(std::is_same<database, CXCompilationDatabase>::value, "forgot to update type");
@@ -88,7 +94,10 @@ namespace
 }
 
 libclang_compile_config::libclang_compile_config()
-: compile_config({}), write_preprocessed_(false), fast_preprocessing_(false)
+: compile_config({}),
+  write_preprocessed_(false),
+  fast_preprocessing_(false),
+  remove_comments_in_macro_(false)
 {
     // set given clang binary
     auto ptr   = CPPAST_CLANG_VERSION_STRING;

src/libclang/preprocessor.cpp

@@ -200,9 +200,15 @@ namespace
     {
         // -x c++: force C++ as input language
         // -E: print preprocessor output
-        // -CC: keep comments, even in macro
         // -dD: keep macros
-        auto flags = std::string("-x c++ -E -CC -dD");
+        auto flags = std::string("-x c++ -E -dD");
+
+        // -CC: keep comments, even in macro
+        // -C: keep comments, but not in macro
+        if (!detail::libclang_compile_config_access::remove_comments_in_macro(c))
+            flags += " -CC";
+        else
+            flags += " -C";
 
         if (macro_file_path)
             // -no*: disable default include search paths