allow float constants to have "e" suffix

src/parser/parser.l

@@ -117,7 +117,7 @@ sizeof              return TOK_SIZEOF;
 '\\f'               (void)'\f'; return TOK_CHAR_CONST;
 [0-9]+([uU][lL]?[lL]?)?              return TOK_INT_CONST;
 0[xX][0-9a-fA-F]+([uU][lL]?[lL]?)?   return TOK_INT_CONST;
-[0-9]*\.[0-9]*[fF]? return TOK_FLOAT_CONST;
+[0-9]*\.[0-9]*[fF]?([eE][0-9]+)?     return TOK_FLOAT_CONST;
 
 \" {
     if (build_string != NULL)