Add a `description` field to target definitions

This is the short description (`64-bit MinGW (Windows 7+)`) including
the platform requirements.

The reason for doing it like this is that this PR will be quite prone to
conflicts whenever targets get added, so it should be as simple as
possible to get it merged. Future PRs which migrate targets are scoped
to groups of targets, so they will not conflict as they can just touch
these.

This moves some of the information from the rustc book into the
compiler.
It cannot be queried yet, that is future work. It is also future work to
fill out all the descriptions, which will coincide with the work of
moving over existing target docs to the new format.

1 files changed, 1 insertions, 0 deletions

diff --git a/compiler/rustc_target/src/spec/base/avr_gnu.rs b/compiler/rustc_target/src/spec/base/avr_gnu.rs
index cd324c94bbe..1e410cea8d6 100644
--- a/compiler/rustc_target/src/spec/base/avr_gnu.rs
+++ b/compiler/rustc_target/src/spec/base/avr_gnu.rs
@@ -8,6 +8,7 @@ use object::elf;
 pub fn target(target_cpu: &'static str, mmcu: &'static str) -> Target {
     Target {
         arch: "avr".into(),
+        description: None,
         data_layout: "e-P1-p:16:8-i8:8-i16:8-i32:8-i64:8-f32:8-f64:8-n8-a:8".into(),
         llvm_target: "avr-unknown-unknown".into(),
         pointer_width: 16,