Add support for CMake for GCC / ARMCC / ARMCLANG

[mbrossard]

This build on #474 (so not that many commits)

I completely rewrote using target_* commands rather than appending variables, this means CMake is much more helpful with escaping flags, and opens the way to a workspace-wide CMake. Armclang support was a little more tedious because it feel like I have to fight against the support in CMake. Using the -o option in build and generate commands allows to pass options to the toolchain build() function, e.g. -o generator=<g> selects the CMake generator, the options for <g> are make (default), ninja, mingw-make, nmake.

Using CMake can be faster with the make back-end than progen's make tool option with workspace (see #480)

[0xc0170]

Master is now unblocked (travis should pass), shall this be rebased?

[mbrossard]

It builds on #474 and I have a lot of fixes and improvements for CMake support in my development branch. What do you think would be appropriate steps/progression? There are a lot of changes that could be put in different blocks in different orders:

• make/armclang support + some additions from @flit (in #474).
• alignement and fixes for make (gcc, armcc and armclang): macro quoting, windows support (in development)
• cmake support for gcc/armcc/armclang (all together or separately?) (this ticket + development)
• build_project for cmake (in development)
• workspace support in make (in development)
• workspace support in cmake (in development)

[flit]

Instead of USE_NINJA, could you add a command line argument to the generate and build subcommands to set the CMake generator?

[mbrossard]

This is changed in a commit on development I did yesterday. It is currently at the API level, but I was thinking something like -o generator=ninja for the command-line. This mechanism could be also useful for make_* toolchains where for instance you might want to call gmake instead of make.

[mbrossard]

* make/armclang support + some additions from @flit (in #474).
* alignement and fixes for make (gcc, armcc and armclang): macro quoting, windows support (in `development`)

This is in #474.

* cmake support for gcc/armcc/armclang (all together or separately?) (this ticket + `development`)
* `build_project` for cmake (in `development`)

This is in #475 (this ticket)

* workspace support in make (in `development`)
* workspace support in cmake (in `development`)

This is in #480.

[mbrossard]

Added mbrossard/project_generator#1 from @flit.

[0xc0170]

This is in #474.

It was merged, shall this be rebased ?

[mbrossard]

Rebased on master