patch 8.2.1676: compiler warnings for function typecast

Problem:    Compiler warnings for function typecast.
Solution:   Add an intermediate cast to "void *".
diff --git a/src/os_unix.c b/src/os_unix.c
index b58138b..6f7a9a4 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -7434,7 +7434,7 @@
 			    )))
 		{
 		    if (string_result == NULL)
-			retval_int = ((STRPROCINT)ProcAdd)(argstring);
+			retval_int = ((STRPROCINT)(void *)ProcAdd)(argstring);
 		    else
 			retval_str = (ProcAdd)(argstring);
 		}
@@ -7456,7 +7456,7 @@
 			    )))
 		{
 		    if (string_result == NULL)
-			retval_int = ((INTPROCINT)ProcAddI)(argint);
+			retval_int = ((INTPROCINT)(void *)ProcAddI)(argint);
 		    else
 			retval_str = (ProcAddI)(argint);
 		}