Need to be able to use multiple compiler flags

[MarceloSalazar]

Duplicate of #389

Description

• Type: Enhancement
• Priority: Major

Enhancement

Reason to enhance/problem with existing solution
Need to have compiler flags e.g., optimisation level, flag warnings as errors etc as configurable parameters.

Suggested enhancement
The configuration may happen in a json file or on the command line along with mbed --compile command."

[ciarmcom]

ARM Internal Ref: IOTMORF-154

[sg-]

Should be implemented by build profiles.