rust: Switch to RUSTC_BOOTSTRAP=1 backdoor instead of nightly

Nightly is messing around with alloc_error_handler and they can't seem
to make up their mind about it, breaking our CI. Just switch to stable
rust with the usual backdoor to enable unstable features (same as the
kernel does).

Signed-off-by: Hector Martin <[email protected]>

Author: marcan

.github/workflows/build.yml

@@ -29,7 +29,7 @@ jobs:
 
       - name: Install nightly rust
         run: |
-          export RUSTUP_TOOLCHAIN=nightly
+          export RUSTUP_TOOLCHAIN=stable
           rustup target install aarch64-unknown-none-softfloat
 
       - name: Build

Makefile

@@ -49,7 +49,7 @@ CFG += RELEASE
 endif
 
 # Required for no_std + alloc for now
-export RUSTUP_TOOLCHAIN=nightly
+export RUSTC_BOOTSTRAP=1
 RUST_LIB := librust.a
 RUST_LIBS :=
 ifeq ($(CHAINLOADING),1)