os400: do not miss some external prototypes

Build procedure extproto() did not strip braces from header files, thus
possibly prepended them to true prototypes. This prevented the prototype to
be recognized as such.
The solution implemented here is to map braces to semicolons, effectively
considering them as potential prototype delimiters.

os400/make-src.sh

@@ -20,7 +20,7 @@ extproto()
             -e '/\/\*/!{'                                               \
             -e '/^#/{s/^.*[^\\]$//;h;d'                                 \
             -e '}'                                                      \
-            -e 's/\\$//'                                                \
+            -e 's/[{}]/;/g;s/\\$//'                                     \
             -e ':loop1'                                                 \
             -e '/;/{'                                                   \
             -e 's/^[^;]*;//;x;s/;.*//'                                  \