[legacy armasm] Unused arguments

[brondani]

Reported by @andbararm:
Assembling a file with legacy armasm syntax causes warnings:

armclang: warning: argument unused during compilation: '-MD' |  '-MT' | '-MF' [-Wunused-command-line-argument]

This is a side effect of Open-CMSIS-Pack/devtools#2144 where the flags for generation of dependency information were introduced.

Note that regardless of any flag the following warning is thrown for legacy files:

Warning: A1950W: The legacy armasm assembler is deprecated. Consider using the armclang integrated assembler instead.

How far and wide should we support armasm legacy?
Alternatives:

• Re-introduce assembly dialects handling as for cbuildgen (AS_ARM, AS_GNU, AS_LEG)
• Set dependency generation flags in individual properties for each file
• Promote the use of armclang assembler instead of armasm.

[jkrech]

No plans at this point to prioritize. The expectation is that projects migrate to GNU assembler and for startup even to C + linker script.