updated for version 7.3.187
Problem:    The RISC OS port has obvious errors and is not being maintained.
Solution:   Remove the RISC OS files and code.
diff --git a/src/memfile.c b/src/memfile.c
index 8769dbc..c87b981 100644
--- a/src/memfile.c
+++ b/src/memfile.c
@@ -1307,7 +1307,7 @@
      * fname cannot be NameBuff, because it must have been allocated.
      */
     mf_set_ffname(mfp);
-#if defined(MSDOS) || defined(MSWIN) || defined(RISCOS)
+#if defined(MSDOS) || defined(MSWIN)
     /*
      * A ":!cd e:xxx" may change the directory without us knowning, use the
      * full pathname always.  Careful: This frees fname!