Fix Arduino CLI preprocess handling in SDCC wrapper

[Copilot]

The arduino-cli_compile_all Actions job was failing during sketch preprocessing and library detection, before normal compilation began. The failure came from the SDCC wrapper not handling Arduino CLI's preprocess invocation shape correctly.

• Root cause

  • arduino-cli invokes the wrapper in preprocess mode (-E) for generated sketch output and library detection.
  • The wrapper treated these calls like regular compiles, which caused:
    • missing preprocessed output files such as sketch_merged.cpp
    • -MF ...libsdetect.d being passed through to SDCC as if it were a normal input/output argument

• Wrapper changes

  • detect preprocess invocations in sdcc.sh
  • strip -MF <depfile> before invoking SDCC
  • write preprocess stdout to the requested Arduino CLI output file
  • when Arduino CLI uses /dev/null for output during lib detection, redirect SDCC's dependency side effects to the depfile stem instead

• Behavior preserved

  • leave normal compile/link flows unchanged
  • skip .rel copy/alignment logic for preprocess-only runs

• Example

  # Arduino CLI preprocess / library-detect style call
  sdcc.sh sdcc sketch.cpp /dev/null re12 -MMD -E -MC -MF sketch.cpp.libsdetect.d
  
  # Wrapper now:
  # - removes -MF from the SDCC argv
  # - preserves preprocess output handling
  # - uses the depfile stem for SDCC's output-side dependency generation