Mbed-cli: separate build subdir for each build profile

[bmcdonnell-ionx]

Feature/behavior request: make the default build dir for mbed compile a subdir under BUILD/. Name the subdir the same as the name of the build profile file, without extension.

[EDIT: revised paths in table.]

e.g.

| Command | Build Dir |
| ------------------------------------------------------------- | -------------------------------------------------- |
| mbed compile | BUILD/<target>/<toolchain>/develop/ |
| mbed compile --profile debug | BUILD/<target>/<toolchain>/debug/ |
| mbed compile --profile=myprofiles/superoptimized-cpp11.json | BUILD/<target>/<toolchain>/superoptimized-cpp11/ |

This way users can switch between build profiles without having to rebuild everything, and without having to specify custom build dirs.

(Re: the first example, mbed-os/tools/profiles/develop.json is the default build profile, right?)

[bmcdonnell-ionx]

I suggest parsing from the build profile filename once it is found on the file system, not from the command line. That way, on a case-insensitive filesystem, e.g. mbed compile --profile debug and mbed compile --profile DEBUG don't create duplicates.

[ciarmcom]

ARM Internal Ref: MBOTRIAGE-679

[0xc0170]

This way users can switch between build profiles without having to rebuild everything, and without having to specify custom build dirs.

I believe this is how some IDE are handling what they call "targets" (=release/debug + flash/ram).

[0xc0170]

I think this is similar to the one #615 (might be duplicate)

[bmcdonnell-ionx]

Closed as dupe of #615.