extra: remove commented out 'X' and 'x' formats

These formats are already covered with 'T' | 'X' in line 571 and 'D' | 'x' in
line 446.
auto merge of #9734 : luisbg/rust/master, r=alexcrichton

These formats are already covered with 'T' | 'X' in line 571 and 'D' | 'x' in
line 446.
testsuite: Two tests for fixed bugs

Closes #7246
Closes #7573
auto merge of #9733 : catamorphism/rust/issues-7246-and-7573, r=alexcrichton

r? anybody Closes #7246
Closes #7573
Implement feature-gating for the compiler

A few features are now hidden behind various #[feature(...)] directives. These
include struct-like enum variants, glob imports, and macro_rules! invocations.

Closes #9304
Closes #9305
Closes #9306
Closes #9331
Add appropriate #[feature] directives to tests