Fix a problem with the erlang grade on Windows.

m4/mercury.m4:
	Only keep the basename of ERLC and ERL if their initial values
	are qualified with directories whose names contains spaces.  This
	avoids build problems on Windows.  (We do the same thing for the
	Java tools.)

m4/mercury.m4

@@ -619,8 +619,24 @@ else
 	mercury_cv_erlang="no"
 fi
 
-AC_SUBST(ERLC)
-AC_SUBST(ERL)
+# On Windows, Erlang/OTP has a high chance of being installed in a path
+# containing spaces.  The simplest solution is to keep only the basename.
+# Everything will still work so long as the executables can be found on the
+# PATH later.
+case "$ERLC" in
+    *" "*)
+        ERLC=`basename "$ERLC"`
+        ;;
+esac
+
+case "$ERL" in 
+    *" "*)
+        ERL=`basename "$ERL"`
+        ;;
+esac
+
+AC_SUBST([ERLC])
+AC_SUBST([ERL])
 ])
 
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