[binutils-gdb] Fix handling of discriminantless univariant enums in Rust; fix bug with encoded enums

[sergiodj+buildbot at sergiodj dot net]

*** TEST RESULTS FOR COMMIT 51a789c3bf3d9b04d3d81493fda7f2514ae43add ***

Author: Manish Goregaokar <manish@mozilla.com>
Branch: master
Commit: 51a789c3bf3d9b04d3d81493fda7f2514ae43add

Fix handling of discriminantless univariant enums in Rust; fix bug with encoded enums

2016-10-27  Manish Goregaokar  <manish@mozilla.com>

gdb/ChangeLog:
    * rust-lang.c (rust_get_disr_info): Treat univariant enums
    without discriminants as encoded enums with a real field
    * rust-lang.c (rust_evaluate_subexp): Handle field access
    on encoded struct-like enums

gdb/testsuite/ChangeLog:
    * simple.rs: Add test for univariant enums without discriminants
    and for encoded struct-like enums
    * simple.exp: Add test expectations