Removing the comment was actually not necessary.
diff --git a/expat/lib/libexpat.def b/expat/lib/libexpat.def
index e442b32..3920bbc 100644
--- a/expat/lib/libexpat.def
+++ b/expat/lib/libexpat.def
@@ -1,3 +1,5 @@
+; DEF file for MS VC++
+
 LIBRARY
 EXPORTS
   XML_DefaultCurrent @1
diff --git a/expat/lib/libexpatw.def b/expat/lib/libexpatw.def
index e442b32..3920bbc 100644
--- a/expat/lib/libexpatw.def
+++ b/expat/lib/libexpatw.def
@@ -1,3 +1,5 @@
+; DEF file for MS VC++
+
 LIBRARY
 EXPORTS
   XML_DefaultCurrent @1