Oops, left in a non-standard multi-line doc string that GCC finds okay
but other compilers don't like.
diff --git a/Modules/structmodule.c b/Modules/structmodule.c
index cb1b36a..065ec6f 100644
--- a/Modules/structmodule.c
+++ b/Modules/structmodule.c
@@ -1208,10 +1208,10 @@
 }
 
 
-static char unpack__doc__[] =
-"unpack(fmt, string) -> (v1, v2, ...)
-Unpack the string, containing packed C structure data, according\n"
-"to fmt.  Requires len(string)==calcsize(fmt).\n\
+static char unpack__doc__[] = "\
+unpack(fmt, string) -> (v1, v2, ...)\n\
+Unpack the string, containing packed C structure data, according\n\
+to fmt.  Requires len(string)==calcsize(fmt).\n\
 See struct.__doc__ for more on format strings.";
 
 static PyObject *