Add uwtable annotation to modules when required

[Darksonn]

When unwind tables are enabled with -Cforce-unwind-tables=y, Rust will annotate all functions with the uwtable annotation. However, this annotation is missing on modules, which leads to incorrect unwind tables being generated by LLVM for constructors (such as asan.module_ctor).

This was discovered because it leads to a crash in Linux when KASAN and dynamic shadow call stack are both enabled. In this scenario, the kernel uses the unwind tables to locate the paciasp and autiasp instructions in each function and patches the machine code at boot to use the shadow call stack instructions instead. However, LLVM's AArch64PointerAuth pass emits DWARF info for paciasp whenever -g is passed, but only emits DWARF info for autiasp when the uwtable attribute is present. Since the uwtable annotation is missing for modules, the relevant directives are generated for only the autiasp instruction in asan.module_ctor, and not for the paciasp instruction. This causes the kernel's dynamic SCS logic to patch the prolouge of asan.module_ctor, but not the epilogue. This leads to a crash as the shadow call stack becomes unbalanced.

The fact that LLVM doesn't use the same condition for whether to emit DWARF information for both instructions may be a separate bug in LLVM.

Relevant issue: llvm/llvm-project#188234

AI assistance was used to determine the root cause of this crash from the observed symptoms, and to write the tests. Also thanks to @samitolvanen and @maurer for debugging this issue.

Similar to this previous PR of mine: #130824

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[Darksonn]

Verified that passing -Zllvm_module_flag=uwtable:u32:2:max to the Linux kernel build fixes the boot failure that triggered this PR.