Merge pull request #4211 from Prthmsh7/fix-hex-float-grammar

Fix for Issue #4149, Added undocumented HexFloat syntax to the specification

Author: dkorpel

spec/lex.dd

@@ -905,6 +905,7 @@ $(GNAME HexFloat):
     $(GLINK HexPrefix) $(GLINK HexDigitsNoSingleUS) $(B .) $(GLINK HexDigitsNoStartingUS) $(GLINK HexExponent)
     $(GLINK HexPrefix) $(B .) $(GLINK HexDigitsNoStartingUS) $(GLINK HexExponent)
     $(GLINK HexPrefix) $(GLINK HexDigitsNoSingleUS) $(GLINK HexExponent)
+    $(GLINK HexPrefix) $(GLINK HexExponent)
 
 $(GNAME HexPrefix):
     $(B 0x)