c_parser: support parenthesized compounds

[JordanYates]

Add support for parenthesized compound statements as per #422.

Below is a source snippet and corresponding generated AST (as generated by ast.show())

void foo()
{
	int a;

	({});
	({ 1; });
	({ 1; 2; });
	int b = ({ 1; });
	int c, d = ({ int x = 1; x + 2; });

	a = ({ int x = 1; 2 * x; });
}

FileAST:
  FuncDef:
    Decl: foo, [], [], []
      FuncDecl:
        TypeDecl: foo, []
          IdentifierType: ['void']
    Compound:
      Decl: a, [], [], []
        TypeDecl: a, []
          IdentifierType: ['int']
      Compound:
      Compound:
        Constant: int, 1
      Compound:
        Constant: int, 1
        Constant: int, 2
      Decl: b, [], [], []
        TypeDecl: b, []
          IdentifierType: ['int']
        Compound:
          Constant: int, 1
      Decl: c, [], [], []
        TypeDecl: c, []
          IdentifierType: ['int']
      Decl: d, [], [], []
        TypeDecl: d, []
          IdentifierType: ['int']
        Compound:
          Decl: x, [], [], []
            TypeDecl: x, []
              IdentifierType: ['int']
            Constant: int, 1
          BinaryOp: +
            ID: x
            Constant: int, 2
      Assignment: =
        ID: a
        Compound:
          Decl: x, [], [], []
            TypeDecl: x, []
              IdentifierType: ['int']
            Constant: int, 1
          BinaryOp: *
            Constant: int, 2
            ID: x

Signed-off-by: Jordan Yates jordan.yates@data61.csiro.au

[eliben]

Thanks for the detailed tests; looks good