Add support for codegen'ing paren exprs and if stmts. We can now codegen:

void test() {
  goto l;

l:
  if (11) {
    j: ;
  }
}

into:

define void @test() {
entry:
        br label %l

l:              ; preds = %entry
        icmp ne i32 11, 0               ; <i1>:0 [#uses=1]
        br i1 %0, label %ifthen, label %ifend

ifthen:         ; preds = %l
        br label %j

j:              ; preds = %ifthen
        br label %ifend

ifend:          ; preds = %j, %l
}

whoa... :)

llvm-svn: 39533