Add compatibilty with rust-stable.

  * Add feature flag for const-fn functionality, which simplifies some
    things and lets this crate run on architectures where atomic CAS
    isn't available (e.g., thumbv6).

  * Remove `const fn` where necessary to compile under rust-stable.

  * BREAKING CHANGE - Change signature of `Handler::replace` to take a
    mutable borrow. This is required because the underlying type is
    now a NonNull, which needs `mut`. The old behavior was never
    desired, but a consequence of trying to avoid `Option` by using a
    default handler.

  * Use lazy_static crate for initialization of Handler/HandlerArray.

  * Specify Sync for Handler. This is not amazing, since it isn't, but
    it's necessary for initialization in static contexts inside
    `lazy_static`. This should be fine, because any actual
    manipulation of the handler is done in unsafe functions.

1 files changed, 2 insertions, 1 deletions

diff --git a/Cargo.toml b/Cargo.toml
index 6d6f192..81c783b 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,12 +14,13 @@ readme = "README.md"
 cortex-m = "~0.6"
 cortex-m-rt = "~0.6"
 compiletest_rs = "~0.3"
+lazy_static = "~1.3"
 
 [target.'cfg(all(target_arch = "arm", target_os = "none"))'.dependencies]
 cortex-m = "~0.6"
 
 [features]
-default = ["isr-32"]
+default = ["isr-32", "compiletest_rs/stable"]
 const-fn = []
 
 # Number of ISR closures to hold in a HandlerTable. This is pretty