YJIT: Make sure rustc's target matches before enabling (#6804)

For people using Rosetta 2 on ARM Macs, it can happen that the
rustc in the PATH compiles for x86_64 while clang is targeting
ARM. We were enabling YJIT in these situations because the test
program compiled fine, but caused linking failure later due to
the architecture mismatch.

Adjust the test program to fail when rustc's target arch is different
from ruby's target arch.

[Bug #19146]

configure.ac

@@ -3744,8 +3744,16 @@ AC_CHECK_PROG(RUSTC, [rustc], [rustc], [no]) dnl no ac_tool_prefix
 dnl check if rustc is recent enough to build YJIT (rustc >= 1.58.0)
 YJIT_RUSTC_OK=no
 AS_IF([test "$RUSTC" != "no"],
-    AC_MSG_CHECKING([whether ${RUSTC} is new enough for YJIT])
-    AS_IF([echo "fn main() { let x = 1; format!(\"{x}\"); }" | $RUSTC - --emit asm=/dev/null 2>/dev/null],
+    AC_MSG_CHECKING([whether ${RUSTC} works for YJIT])
+    YJIT_TARGET_ARCH=
+    AS_CASE(["$target_cpu"],
+        [arm64|aarch64], [YJIT_TARGET_ARCH=aarch64],
+        [x86_64], [YJIT_TARGET_ARCH=x86_64],
+    )
+    dnl Fails in case rustc target doesn't match ruby target.
+    dnl Can happen on Rosetta, for example.
+    AS_IF([echo "#[cfg(target_arch = \"$YJIT_TARGET_ARCH\")]\n fn main() { let x = 1; format!(\"{x}\"); }" |
+            $RUSTC - --emit asm=/dev/null 2>/dev/null],
         [YJIT_RUSTC_OK=yes]
     )
     AC_MSG_RESULT($YJIT_RUSTC_OK)