Revert the regression, add a GBA target to avoid this again

.travis.yml

@@ -64,6 +64,24 @@ matrix:
       env: TARGET=thumbv7em-none-eabi NORUN=1 NOSTD=1 NO_DOCKER=1
     - name: "thumbv7em-none-eabihf - build libcore only"
       env: TARGET=thumbv7em-none-eabihf NORUN=1 NOSTD=1 NO_DOCKER=1
+    - name: "Game Boy Advance - build libcore only"
+      env: NORUN=1 NOSTD=1 NO_DOCKER=1
+      install: cargo install xargo
+      script:
+        # Obtain the devkitPro tools, using `target/` as a temp directory. This
+        # is required because we need to use their linker. `lld` uses the `BLX`
+        # instruction, which was not available in thumb state code until ARMv5.
+        - mkdir -p target
+        - cd target
+        - wget https://github.com/devkitPro/pacman/releases/download/devkitpro-pacman-1.0.1/devkitpro-pacman.deb
+        - sudo dpkg -i devkitpro-pacman.deb
+        - sudo dkp-pacman -Sy
+        - sudo dkp-pacman -Syu
+        - sudo dkp-pacman -S -v --noconfirm gba-tools devkitARM
+        - export PATH="$PATH:/opt/devkitpro/devkitARM/bin"
+        - export PATH="$PATH:/opt/devkitpro/tools/bin"
+        - cd ..
+        - xargo build --all --target=ci/gba.json
     - name: "Documentation"
       install: true
       script: ci/dox.sh

ci/gba.json

@@ -0,0 +1,34 @@
+{
+  "abi-blacklist": [
+    "stdcall",
+    "fastcall",
+    "vectorcall",
+    "thiscall",
+    "win64",
+    "sysv64"
+  ],
+  "arch": "arm",
+  "atomic-cas": false,
+  "cpu": "arm7tdmi",
+  "data-layout": "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64",
+  "emit-debug-gdb-scripts": false,
+  "env": "agb",
+  "executables": true,
+  "features": "+soft-float,+strict-align",
+  "linker": "arm-none-eabi-ld",
+  "linker-flavor": "ld",
+  "linker-is-gnu": true,
+  "llvm-target": "thumbv4-none-agb",
+  "os": "none",
+  "panic-strategy": "abort",
+  "pre-link-args": {
+    "ld": [
+      "-Tlinker.ld"
+    ]
+  },
+  "relocation-model": "static",
+  "target-c-int-width": "32",
+  "target-endian": "little",
+  "target-pointer-width": "32",
+  "vendor": "nintendo"
+}

crates/core_arch/src/acle/registers/aarch32.rs

@@ -1,5 +1,9 @@
 /// Application Program Status Register
 pub struct APSR;
 
-#[cfg(any(not(target_feature = "thumb-mode"), target_feature = "v6t2"))]
-rsr!(APSR);
+// Note (@Lokathor): Because this breaks the use of Rust on the Game Boy
+// Advance, this change must be reverted until Rust learns to handle cpu state
+// properly. See also: https://github.com/rust-lang-nursery/stdsimd/issues/702
+
+//#[cfg(any(not(target_feature = "thumb-state"), target_feature = "v6t2"))]
+//rsr!(APSR);