Add include guards that allow multiple includes of `OptParser.td`. This
is helpful when defining multiple sets of options in multiple files.
For example, a user could define a `HelpOptions.td` file that defines
only `-h` and `--help`:
```
// HelpOptions.td
include "llvm/Option/OptParser.td"
def HelpOptionGroup : OptionGroup<"Help Options">;
def help : Flag<["--", "-"], "help">, Group<HelpOptionGroup>,
Flags<[]>;
def : Flag<["-"], "h">, Group<HelpOptionGroup>, Flags<[]>, Alias<help>;
```
This file could then be included into any TableGen file that wishes to
define these options:
```
// MyOptions.td
include "llvm/Option/OptParser.td"
def MyOptionGroup : OptionGroup<"My Options">;
// ...define my options.
// And also define `-h` and `--help`:
include "HelpOptions.td"
```
This currently isn't possible, because this would result in
`OptParser.td` being included twice. Alternatively, the include of
`OptParser.td` in the `HelpOptions.td` example above could be removed,
but then `llvm-tblgen --gen-opt-parser-defs HelpOptions.td` would fail
(because the `OptionGroup` and `Option` records are defined in
`OptParser.td`).
Reviewed By: rriddle
Differential Revision: https://reviews.llvm.org/D153915
//
//===----------------------------------------------------------------------===//
+#ifndef LLVM_OPTION_OPTPARSER_TD
+#define LLVM_OPTION_OPTPARSER_TD
+
// Define the kinds of options.
class OptionKind<string name, int precedence = 0, bit sentinel = false> {
// aren't duplicated).
def INPUT : Option<[], "<input>", KIND_INPUT>;
def UNKNOWN : Option<[], "<unknown>", KIND_UNKNOWN>;
+
+#endif // LLVM_OPTION_OPTPARSER_TD