Auto merge of #3915 - RalfJung:target-json-test, r=RalfJung

switch custom target JSON test to a less exotic target

We used to test an AVR target here, but while it is nice to test a 16bit target, it is also currently the case that rustc CI does not even check that libcore builds on a 16bit target -- and we don't want Miri to be in the game of maintaining that support. (See rust-lang/rust#130818.)

So let's use a tier 2 target as the basis for testing a custom JSON target.

(FWIW, we also test wasm32-wasip2 which is tier 3, but I expect it will become tier 2 Soon-ish.)

ci/ci.sh

@@ -159,8 +159,7 @@ case $HOST_TARGET in
     TEST_TARGET=wasm32-unknown-unknown run_tests_minimal no_std empty_main wasm # this target doesn't really have std
     TEST_TARGET=thumbv7em-none-eabihf  run_tests_minimal no_std
     # Custom target JSON file
-    # FIXME: disabled due to <https://github.com/rust-lang/rust/issues/130818>.
-    #TEST_TARGET=tests/avr.json MIRI_NO_STD=1 run_tests_minimal no_std
+    TEST_TARGET=tests/x86_64-unknown-kernel.json MIRI_NO_STD=1 run_tests_minimal no_std
     ;;
   i686-pc-windows-msvc)
     # Host

tests/x86_64-unknown-kernel.json

@@ -0,0 +1,24 @@
+{
+  "llvm-target": "x86_64-unknown-none",
+  "target-endian": "little",
+  "target-pointer-width": "64",
+  "target-c-int-width": "32",
+  "data-layout": "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
+  "arch": "x86_64",
+  "os": "none",
+  "env": "",
+  "vendor": "unknown",
+  "linker": "rust-lld",
+  "linker-flavor": "gnu-lld",
+  "features": "-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2,+soft-float",
+  "dynamic-linking": false,
+  "executables": true,
+  "relocation-model": "static",
+  "code-model": "kernel",
+  "disable-redzone": true,
+  "frame-pointer": "always",
+  "exe-suffix": "",
+  "has-rpath": false,
+  "no-default-libraries": true,
+  "position-independent-executables": false
+}