Add static declaration to function only used in same compilation unit.

src/pio_impl.h

@@ -96,7 +96,6 @@ void pioWriterAIO(void);
 #endif
 
 /* pio_posixfpguardsendrecv.c */
-void      fpgPOSIXFPGUARDSENDRECV ( void );
 int       fowPOSIXFPGUARDSENDRECV ( const char * );
 int       fcPOSIXFPGUARDSENDRECV ( int );
 size_t    fwPOSIXFPGUARDSENDRECV ( int, int, const void *, size_t );

src/pio_posixfpguardsendrecv.c

@@ -161,7 +161,8 @@ compareNamesAPF(void *v1, void *v2)
 
 /***************************************************************/
 
-void fpgPOSIXFPGUARDSENDRECV ( void )
+static void
+fpgPOSIXFPGUARDSENDRECV(void)
 {
   int i, source, iret;
   struct fileOpTag rtag;