Fixed/added missing/wrong function prototypes and made internal
functions static.

diff --git a/dlls/comctl32/header.c b/dlls/comctl32/header.c
index 97bd3e9..42a633c 100644
--- a/dlls/comctl32/header.c
+++ b/dlls/comctl32/header.c
@@ -1442,7 +1442,7 @@
 }
 
 
-LRESULT WINAPI
+static LRESULT WINAPI
 HEADER_WindowProc (HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {
     switch (msg) {