Insert new line to separate preprocessor directive

Otherwise it seems clang-format recognizes this as a multi-line
preprocessor directive, strange, but preventable.

(cherry picked from commit 3c673965)

src/backend/gporca/libgpos/include/gpos/common/CSyncPool.h

@@ -238,6 +238,7 @@ namespace gpos
     #ifdef GPOS_DEBUG
                             BOOL recycled =
     #endif // GPOS_DEBUG
+
                             // unset the reserve bit - must succeed
                             UnsetBit(&m_objs_reserved[elem_offset], bit_val);