Remove systematic 'legacyalign' warning

[jeromecoutant]

Description of defect

With ARMC6 we got a systematic warning in logs:

[Warning] @0,0: L3912W: Option 'legacyalign' is deprecated.
[Warning] @0,0: L3912W: Option 'legacyalign' is deprecated.
[Warning] @0,0: L3912W: Option 'legacyalign' is deprecated.

#14151 tried without any success

@0xc0170

Target(s) affected by this defect ?

all

Toolchain(s) (name and version) displaying this defect ?

ARMC6

What version of Mbed-os are you using (tag or sha) ?

mbed-os-6.7.0

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

NA

How is this defect reproduced ?

All compilation

[ciarmcom]

@jeromecoutant thank you for raising this issue.Please take a look at the following comments:

Could you add some more detail to the description? A good description should be at least 25 words.

NOTE: If there are fields which are not applicable then please just add 'n/a' or 'None'. This indicates to us that at least all the fields have been considered.
Please update the issue header with the missing information, the issue will not be mirrored to our internal defect tracking system or investigated until this has been fully resolved.

[ciarmcom]

Thank you for raising this detailed GitHub issue. I am now notifying our internal issue triagers.
Internal Jira reference: https://jira.arm.com/browse/IOTOSM-3464

[0xc0170]

Reference for the recent clean up that uncovered lot of holes in targets: #10373