CI: replace compiletest-rs with trybuild

We use compiletest to run compile-fail tests but compiletest depends on compiler
internals so it breaks every now and then and requires nightly. With trybuild we
can also run compile-fail tests but it works on stable and it already has
reached version 1.0

ui/single/exception-invalid.stderr

@@ -3,6 +3,3 @@ error: only exceptions with configurable priority can be used as hardware tasks
   |
 6 |     fn nmi(_: nmi::Context) {}
   |        ^^^
-
-error: aborting due to previous error
-

ui/single/exception-systick-used.stderr

@@ -3,6 +3,3 @@ error: this exception can't be used because it's being used by the runtime
   |
 6 |     fn sys_tick(_: sys_tick::Context) {}
   |        ^^^^^^^^
-
-error: aborting due to previous error
-

ui/single/extern-interrupt-not-enough.stderr

@@ -3,6 +3,3 @@ error: not enough `extern` interrupts to dispatch all software tasks (need: 1; g
   |
 6 |     fn a(_: a::Context) {}
   |        ^
-
-error: aborting due to previous error
-

ui/single/extern-interrupt-used.stderr

@@ -3,6 +3,3 @@ error: `extern` interrupts can't be used as hardware tasks
   |
 5 |     #[task(binds = UART0)]
   |                    ^^^^^
-
-error: aborting due to previous error
-

ui/single/locals-cfg.stderr

@@ -28,6 +28,10 @@ error[E0425]: cannot find value `FOO` in this scope
 44 |         FOO;
    |         ^^^ not found in this scope
 
-error: aborting due to 5 previous errors
+error: duplicate lang item in crate `panic_halt`: `panic_impl`.
+  |
+  = note: first defined in crate `std`.
 
-For more information about this error, try `rustc --explain E0425`.
+error: duplicate lang item in crate `panic_semihosting`: `panic_impl`.
+  |
+  = note: first defined in crate `panic_halt`.

ui/single/resources-cfg.stderr

@@ -117,7 +117,3 @@ error[E0609]: no field `o5` on type `uart1Resources<'_>`
    |                     ^^ unknown field
    |
    = note: available fields are: `__marker__`
-
-error: aborting due to 15 previous errors
-
-For more information about this error, try `rustc --explain E0609`.

ui/single/task-priority-too-high.stderr

@@ -1,9 +1,13 @@
+warning: unused import: `rtfm::app`
+ --> $DIR/task-priority-too-high.rs:3:5
+  |
+3 | use rtfm::app;
+  |     ^^^^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` on by default
+
 error[E0080]: evaluation of constant value failed
  --> $DIR/task-priority-too-high.rs:5:1
   |
 5 | #[rtfm::app(device = lm3s6965)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to subtract with overflow
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0080`.