Declare $rtoi in system.sft instead of the sys_funcs table.

The sys_funcs table should be left to those functions that are handled
internally by the compiler. Really, the internal sys_funcs table is a
legacy from the days before the compiler supported system function
tables in the .sft format.

sys_funcs.cc

@@ -34,7 +34,6 @@ static const struct sfunc_return_type sfunc_table[] = {
       { "$bitstoreal", IVL_VT_REAL,   1, 0 },
       { "$itor",       IVL_VT_REAL,   1, 0 },
       { "$realtobits", IVL_VT_LOGIC, 64, 0 },
-      { "$rtoi",       IVL_VT_LOGIC, 32, 0 },
       { "$time",       IVL_VT_LOGIC, 64, 0 },
       { "$stime",      IVL_VT_LOGIC, 32, 0 },
       { "$simtime",    IVL_VT_LOGIC, 64, 0 },

vpi/system.sft

@@ -4,6 +4,7 @@
 #
 
 $random            vpiSysFuncInt
+$rtoi              vpiSysFuncInt
 $urandom           vpiSysFuncSized 32 unsigned
 $urandom_range     vpiSysFuncSized 32 unsigned
 $dist_uniform      vpiSysFuncInt