Merge pull request #13085 from pea-pod/remove-deprecated-mbed-assert ...

Change MBED_STATIC_ASSERTs version for built-in

CMake: Use relative paths to list source files and directories ...

The absolute path is still required for listing linker
files as they are referenced from a function in the top
level CMake input source file.

CMake: add mbed-os and mbed-baremetal targets ...

mbed-os consists of mbed-core and mbed-rtos
mbed-baremetal consists of mbed-core

The main change is for mbed-core. Changing from object library to be interface. This way it allows us to do the above to have 2 main targets for users to use.

This should be backward compatible change as mbed-os target we used contains the same files/options as previously set.

CMake: Rename CMake targets ...

* mbed-os renamed mbed-core
* mbed-os-<COMPONENT> renamed mbed-<COMPONENT>

CMake: Add support for platform dir

Change MBED_STATIC_ASSERTs version for built-in

mstd_mutex: Add missing Chrono bits

Remove ARMC5 reference from Mbed OS platform

Add mstd_new for mstd::launder ...

Increasingly clever compilers can hit funny aliasing problems with
object stores like mbed::Callback. Add access to the C++17 launder
facility.

Add mstd::is_constant_evaluated ...

GCC 9 and sufficiently-new Clang (including ARM Compiler 6.13) give us
access to the C++20 (draft) `is_constant_evaluated` test. Allows us to
restrict code to compile-time only.

This is particularly useful when using assembler intrinsics, which the
compiler cannot optimise or compile-time evaluate. It allows us to write
something like

    constexpr uint32_t reverse_bits(uint32_t x)
    {
        if (is_constant_evaluated(x)) {
            // C code to do calculation here
            return x;
        } else {
            // an assembler intrinsic that cannot be optimised
            return __RBIT(x);
        }
    }

This can then be totally compile-time given a constant input.

(In this example, ultimately it would be a good idea to include this
functionality in CMSIS's GCC `__RBIT`, which needs it because GCC
requires use of assembler. Clang implements `__RBIT` as a built-in,
meaning it can already compute it at compile-time, so does not benefit.).

Explicit pinmap - fix style

mstd_cstddef: add C support and macros for C++11

mbed_retarget: Add a minimal console implementation to provide basic functionalities ...

The retarget code allocates an array of FileHandle* for console and file
handling (filehandles). A tiny target only needs a console (putc/getc).
There is no need for file handling.

The POSIX layer and the array of FileHandle* is not required for small
targets that only need a console ; this code is optionally compiled
out if the configuration parameter platform.stdio-minimal-console-only is
set to `"true"`.

mstd_iterator: correct comments

mstd_utility: add missing integer_sequence helpers

Add <mstd_tuple> and ARMC5 <tuple> ...

tuples will be useful for things like `mbed::Event` and
`mbed::Callback` - storing parameter packs from variadic templates.

Create a C++14(ish) `<tuple>` for ARMC5, and a `<mstd_tuple>` that
adds `apply` and `make_from_tuple` from C++17.

mstd::not_fn - fix declaration

ARMC5 std::reference_wrapper - drop dead code

Fix cxxsupport/README.md typo

ARMC5 <array>: Add tuple interface

ARMC5 <array>: add comparison operators

ARMC5 <array>: remove not-working constexpr

ARMC5 <array>: permit zero size

Add C++17 uninitialized storage ops

Add ARMC5 unique_ptr ...

Standard library implementation should be fine for other toolchains.

Move Atomic.h to <mstd_atomic> ...

`mbed::Atomic<T>` becomes `mstd::atomic<T>`, alongside the other
standard C++ library lookalikes.

Add <mstd_mutex> ...

Add add-standard-as-possible version of C++11 <mutex>.

A lot of the stuff in there is generic, but the actual mutex classes and
call_once need to interface with the OS.

For those, they're not available in ARMC5 or IAR; retargetting would be
necessary for ARMC6 and GCC, and I've yet to investigate how whether
that's possible. So for now I'm using local implementations.

Although `Mutex` in principle could support `timed_mutex` and
`recursive_timed_mutex`, we don't have `chrono` for the time parameters,
so hold off for now.

For the generic stuff like mstd::unique_lock, they are aliased to
std::unique_lock where possible.

Split mbed_cxxsupport.h up - add namespace mstd ...

Regularise the C++ support glue, adding `<mstd_type_traits>` etc.

These include the base toolchain file, backfill `namespace std` as much
as possible for ARM C 5, and then arrange to create unified
`namespace mstd`, which can incorporate toolchain bypasses
(eg `mstd::swap` for ARM C 5, or `mstd::atomic`), and include local
implementations of post-ARM C++14 stuff.

All APIs in `namespace mstd` are intended to function as their
`namespace std` equivalent, and their presence there indicates they
are functional on all toolchains, and should be safe to use in
an Mbed OS build (including not unreasonable memory footprint).

See README.md for more info.