clang is smart enough to notice a variable is set but not used,
but these variable are used for testing purposes. Mark one as
unused, and convert the other to a DoNotOptimize.
Bug: 197240255
Test: Compiles without warnings.
Test: Ran unit tests on coral hwasan build.
Change-Id: Ibc873e477355a702579e5a680780c77db0c58046
* TTYDEF_OFLAG referred to the BSD OXTABS constant instead of the Linux XTABS,
so references to it wouldn't compile.
* CEOL was incorrect (compared to `stty -a`).
* ttydefchars wouldn't compile (removed rather than attempt to fix something
of unclear utility).
Bug: http://b/63145226
Test: new test
Change-Id: I823e5eaab789cafd2eeea03f77ea553346822f74