Fix compilation errors on armv6k-nintendo-3ds. (#1027)

Author: sunfishcode

.github/workflows/main.yml

@@ -222,6 +222,8 @@ jobs:
     #- run: cargo check -Z build-std --target=riscv32imc-esp-espidf --features=all-apis
     - run: cargo check -Z build-std --target=aarch64-unknown-nto-qnx710 --features=all-apis
     - run: cargo check -Z build-std --target=x86_64-pc-nto-qnx710 --features=all-apis
+    # Temporarily disable --features=all-apis, which doesn't build yet.
+    - run: cargo check -Z build-std --target=armv6k-nintendo-3ds
     # Temporarily disable armv7-sony-vita-newlibeabihf due to std using SOMAXCONN.
     #- run: cargo check -Z build-std --target=armv7-sony-vita-newlibeabihf --features=all-apis
     # `std` doesn't appear to build on AIX yet, so test in `no_std` mode.