Fix fileModifiedTime on 32 bit systems

Can't use MKBIGI for the result, since that'll be a negative number for
the current time! So use MKBIGUI instead to ensure it stays unsigned.

libs/prelude/Prelude/File.idr

@@ -150,7 +150,8 @@ do_getFileAccessTime h =
 private
 do_getFileModifiedTime : Ptr -> IO Integer
 do_getFileModifiedTime h = 
-   do MkRaw i <- foreign FFI_C "fileModifiedTime" (Ptr -> IO (Raw Integer)) h
+   do vm <- getMyVM
+      MkRaw i <- foreign FFI_C "fileModifiedTime" (Ptr -> Ptr -> IO (Raw Integer)) vm h
       pure i
 
 private
@@ -175,7 +176,7 @@ export
 fileModifiedTime : File -> IO (Either FileError Integer)
 fileModifiedTime (FHandle h)
     = do s <- do_getFileModifiedTime h
-         if (s < 0)
+         if (s == -1)
             then Left <$> getFileError
             else pure (Right s)
 

rts/idris_stdfgn.c

@@ -74,13 +74,13 @@ VAL fileAccessTime(void* h) {
     }
 }
 
-VAL fileModifiedTime(void* h) {
+VAL fileModifiedTime(VM* vm, void* h) {
     FILE* f = (FILE*)h;
     int fd = fileno(f);
 
     struct stat buf;
     if (fstat(fd, &buf) == 0) {
-        return MKBIGI(buf.st_mtime);
+        return MKBIGUI(vm, buf.st_mtime);
     } else {
         return MKBIGI(-1);
     }

rts/idris_stdfgn.h

@@ -18,7 +18,7 @@ int fileSize(void* h);
 
 // Return a negative number if not a file (e.g. directory or device)
 VAL fileAccessTime(void* h);
-VAL fileModifiedTime(void* h);
+VAL fileModifiedTime(VM* vm, void* h);
 VAL fileStatusTime(void* h);
 
 void* idris_dirOpen(char* dname);