no_debug and omit_gdb_pretty_printer_sections attributes exist and are ungated

[huonw]

This compiles without a peep from the compiler:

#[no_debug]
#[omit_gdb_pretty_printer_section]
fn main() {}

The later especially seems to be purely designed for the rust testsuite, so should probably be feature gated.

(Nominating for more discussion and some sort of priority: if the decision is made to feature gate them,fixing this should just involve changing a few lines of src/libsyntax/feature_gate.rs and then adding the appropriate feature(...)s to the tests that use them.)

[alexispurslane]

Should someone implement this?

[nikomatsakis]

These should both be feature-gated.

[nikomatsakis]

triage: P-medium

[nikomatsakis]

Tagging with E-mentor -- I'm happy to mentor this. (nmatsakis on IRC)