fix: skip ARM unaligned shim during dependency generation

[messense]

ARM compiler invocations using -M or -MM, such as Jemalloc's Makefile dependency generation, were treated as linking commands and received an extra aeabi_unaligned.c input. With a single -o output, Zig rejected the resulting command with cannot specify -o when generating multiple output files.

Skip the shim for both dependency-only modes. Keep injecting it for linking, including -MD/-MMD, which generate dependencies as a side effect. Regression tests exercise the CLI argument path and cover both behaviors plus the existing -c/-E/-S exclusions.

Validation:

• cargo test: 59 tests passed; the new dependency-generation test failed before the fix.
• Real Zig 0.16.0 ARM -M and -MM invocations with the reported CPU flag successfully generated dependency files after the fix.
• cargo fmt --all --check and git diff --check: passed.
• cargo clippy --all-targets --all-features -- -D warnings: blocked by five pre-existing warnings in unchanged code (useless_conversion, useless_borrows_in_formatting, and chunks_exact_to_as_chunks).

Fixes #478.