Restored mbed target --supported behavior

[cmonr]

Issue reference: #557

[screamerbg]

The underlying problem is the introduction of the matrix parameter, which breaks for older releases of Mbed OS (5.1-5.4.7), basically all releases since July 2016 til July 2017. See #575.

This PR doesn't fix it (rather makes it worse). Appropriate fix should revert the matrix behavior introduced in #460 which breaks backwards compatiblity. Notice that make.py doesn't require the matrix param in mbed-os-5.5, therefore this looks like a safe approach

/tmp/1/test-program:$ mbed update mbed-os-5.5.7
/tmp/1/test-program:$ /usr/bin/python -u /private/tmp/1/test-program/mbed-os/tools/make.py -S 
+----------------------+-----------+-----------+-----------+-----------+-----------+
| Target               | mbed OS 2 | mbed OS 5 |    ARM    |  GCC_ARM  |    IAR    |
+----------------------+-----------+-----------+-----------+-----------+-----------+
| ARCH_PRO             | Supported | Supported | Supported | Supported | Supported |
+----------------------+-----------+-----------+-----------+-----------+-----------+

[snip]

Supported targets: 92

[theotherjimmy]

@cmonr @screamerbg We may be able to solve this by passing nothing when the argument to -S/--supported is "matrix", as this is the default, and the old behavior.

[theotherjimmy]

@screamerbg Could you advise us on how to add a test that verifies that we do this in a backwards compatible way?

Differing to @screamerbg

[screamerbg]

@cmonr could you change this PR so it removes "matrix" as a default argument passed to the underlying OS tools? Then align what's being passed through either mbed compile -S and mbed target -S. Does this make sense?

[screamerbg]

@cmonr Regarding how to test supported, perhaps check the circleCI file, and after mbed new . add something like
mbed target -S
mbed compile -S
mbed update mbed-os-5.5.1
mbed target -S
mbed compile -S
mbed update mbed-os-5.4.1
mbed target -S
mbed compile -S
mbed update mbed-os-5.3.1
mbed target -S
mbed compile -S
mbed update mbed-os-5.2.1
mbed target -S
mbed compile -S
mbed update mbed-os-5.1.1
mbed target -S
mbed compile -S

[screamerbg]

@theotherjimmy Perhaps the same test can be invoked for mbed export -S?

[cmonr]

@screamerbg Well that's amusing. Regarding how to test, that's effectively what I'm doing right now, except I sped it up by having separate directories checked out to their appropriate versions.

[screamerbg]

@cmonr No pretty but it would do the job. You can make it look neat if you iterate through mbed releases (once it lands to master), checkout every MINOR.1 release and run mbed compile -S, mbed export -S and mbed target -S

[cmonr]

@screamerbg Any particular reason why MINOR.1 instead of MINOR.0? Just curious.

[cmonr]

Don't merge yet until tests are written (tomorrow).

Tested using mbed compile -S, mbed target -S, mbed toolchain -S, and mbed export -S on mbed-os-5.x.0 versions, and latest version.

Looking for guidance from @mbartling on how to test for his features.

[screamerbg]

@cmonr if I'm not mistaken, one of the very first versions of mbed OS had the exporters broken in the x.0 release.

[screamerbg]

@cmonr Any update on this?

[cmonr]

@screamerbg The tests have been added in. I didn't find any issues with exporting from 5.1.0 and up.

[screamerbg]

LGTM. Thanks @cmonr