Remove redundant call to msDebugInitFromEnv (MapServer#4522)

`msSetup()` already calls `msDebugInitFromEnv()`.

Specify correct "C" linkage in `cgiutil.h`

`cgiutil.h` is the only file included by `mapserver.h` which defines
symbols and which isn't wrapped by `extern "C"`: its symbols end up in
`libmapserver` and without this fix linking against them in C++ fails.

closes MapServer#4522

Author: Homme Zwaagstra

cgiutil.h

@@ -32,6 +32,9 @@
 #ifndef CGIUTIL_H
 #define CGIUTIL_H
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 #if defined(_WIN32) && !defined(__CYGWIN__)
 #  define MS_DLL_EXPORT     __declspec(dllexport)
@@ -93,4 +96,8 @@ MS_DLL_EXPORT cgiRequestObj *msAllocCgiObj(void);
 MS_DLL_EXPORT void msFreeCgiObj(cgiRequestObj *request);
 #endif /*SWIG*/
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* CGIUTIL_H */

mapserv.c

@@ -140,10 +140,12 @@ int main(int argc, char *argv[])
   struct mstimeval execstarttime, execendtime;
   struct mstimeval requeststarttime, requestendtime;
   mapservObj* mapserv = NULL;
-  msSetup();
 
-  /* Use MS_ERRORFILE and MS_DEBUGLEVEL env vars if set */
-  if( msDebugInitFromEnv() != MS_SUCCESS ) {
+  /* -------------------------------------------------------------------- */
+  /*      Initialize mapserver.  This sets up threads, GD and GEOS as     */
+  /*      well as using MS_ERRORFILE and MS_DEBUGLEVEL env vars if set.   */
+  /* -------------------------------------------------------------------- */
+  if( msSetup() != MS_SUCCESS ) {
     msCGIWriteError(mapserv);
     msCleanup(0);
     exit(0);