test(asm): global asm runs under the JIT (sx run), not just AOT

Adds examples/1653-platform-asm-global-jit.sx — a module-scope asm { … }
block executed via `sx run` (no `aot`). sx run compiles the module to an
in-memory object (the integrated assembler assembles the `module asm`
into it), then ORC relocates and runs it, so a module-asm symbol IS
resolvable at JIT main execution — the long-assumed "AOT only" limit was
stale. Sibling of 1648 (same feature via AOT). Locks current behavior
(exit 42); no compiler change.

examples/1653-platform-asm-global-jit.sx

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+// ASM stream — global (module-scope) `asm { … }` executed via the JIT (`sx run`),
+// NOT AOT. `sx run` compiles the whole module to an in-memory object (the
+// integrated assembler assembles the `module asm` block into it), then ORC
+// relocates and runs it — so a module-asm symbol IS resolvable at JIT main
+// execution, just like a normal symbol. The only path that can't see it is a
+// COMPILE-TIME `#run` call (the interpreter resolves externs via host dlsym; the
+// symbol isn't linked yet — see 1654). Sibling of 1648 (which exercises the same
+// feature via AOT). aarch64-macos-pinned; ir-only elsewhere.
+asm {
+    #string ASM
+.global _my_sub
+_my_sub:
+    sub x0, x0, x1
+    ret
+ASM,
+};
+
+my_sub :: (a: i64, b: i64) -> i64 extern;
+
+main :: () -> i64 {
+    return my_sub(44, 2);   // 42, computed by the global-asm routine, under JIT
+}

examples/expected/1653-platform-asm-global-jit.build

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+{ "target": "macos" }

examples/expected/1653-platform-asm-global-jit.exit

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+42

examples/expected/1653-platform-asm-global-jit.ir

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+
+module asm ".global _my_sub"
+module asm "_my_sub:"
+module asm "    sub x0, x0, x1"
+module asm "    ret"
+
+; Function Attrs: nounwind
+declare i64 @my_sub(i64, i64) #0
+
+; Function Attrs: nounwind
+define i32 @main() #0 {
+entry:
+  %call = call i64 @my_sub(i64 44, i64 2)
+  %ca.tr = trunc i64 %call to i32
+  ret i32 %ca.tr
+}

examples/expected/1653-platform-asm-global-jit.stderr

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+

examples/expected/1653-platform-asm-global-jit.stdout

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+