This is required for DEBUG=1 builds when MICROPY_FLOAT_IMPL=double.

Thanks to Andrew Leech.

This provides a double variant of the float copysignf from libm/math.c
which is required for DEBUG=1 builds when MICROPY_FLOAT_IMPL=double

pyb.mount(None, mountpoint) functionality is also removed and replaced by
uos.umount.

pyb.umount(None, mountpoint) no longer works.

Changes made:
- make use of MP_OBJ_TO_PTR and MP_OBJ_FROM_PTR where necessary
- fix shadowing of index variable i, renamed to j
- fix type of above variable to size_t to prevent comparison warning
- fix shadowing of res variable
- use "(void)" instead of "()" for functions that take no arguments

And thus be buildable again.

This commit implements PEP479 which disallows raising StopIteration inside
a generator to signal that it should be finished.  Instead, the generator
should simply return when it is complete.

See https://www.python.org/dev/peps/pep-0479/ for details.

This part is functionally similar to STM32F767xx (they share a datasheet)
so support is generally comparable.  When adding board support the
stm32f767_af.csv and stm32f767.ld should be used.

Instead of redirecting to str.__mod__(), use str.format() in this case.

Default is enabled, disabled for minimal builds. Saves 1296 bytes on x86,
976 bytes on ARM.

In 0e80f345 the inplace operations __iadd__
and __isub__ were made unconditionally available, so the comment about this
section is changed to reflect that.

The intention of oflush() is to flush the "fast SPI" command itself so that
the SPI object is ready to use when the function returns.

Changes made:
- fix DMA_SUB_INSTANCE_AS_UINT8
- fix dma_id numbers in dma_descr_t
- add F0 DMA IRQ handlers
- set DmaBaseAddress and ChannelIndex when reinit'ing

Fixes issue #4113.

Loading a pointer by indexing into the native function table mp_fun_table,
rather than loading an immediate value (via a PC-relative load), uses less
code space.

Viper functions will now capture the globals at the point they were defined
and use these globals when executing.

Old globals are now stored in the second slot (ip in mp_code_state_t) to
make things simpler for viper.

This commit makes viper functions have the same signature as native
functions, at the level of the emitter/assembler.  This means that viper
functions can now be wrapped in the same uPy object as native functions.

Viper functions are now responsible for parsing their arguments (before it
was done by the runtime), and this makes calling them more efficient (in
most cases) because the viper entry code can be custom generated to suit
the signature of the function.

This change also opens the way forward for viper functions to take
arbitrary numbers of arguments, and for them to handle globals correctly,
among other things.

Now that the compiler can store the results of the viper types in the
scope, the viper parameter annotation compilation stage can be merged with
the normal parameter compilation stage.

In viper mode, the type of the argument is now stored in id_info->flags.

Instead this return type is now stored in the scope_flags.

The native emitter can easily determine the mode via scope->emit_options.

With 5 arguments to mp_arg_check_num(), some architectures need to pass
values on the stack.  So compressing n_args_min, n_args_max, takes_kw into
a single word and passing only 3 arguments makes the call more efficient,
because almost all calls to this function pass in constant values.  Code
size is also reduced by a decent amount:

   bare-arm:  -116
minimal x86:   -64
   unix x64:  -256
unix nanbox:  -112
      stm32:  -324
     cc3200:  -192
    esp8266:  -192
      esp32:  -144

This issue was brought up by BramPeters in the forum:
https://forum.micropython.org/viewtopic.php?p=30066

If DTTOIF() macro is not defined, the code refers to MP_S_IFDIR, etc.
symbols defined in extmod/vfs.h, so should include it.

This fixes build for Android.

Added cmake_minimum_required and updated target_link_libraries directives.

net_config subsystem was split off from net_app, and as a result, settings
need renaming from CONFIG_NET_APP_* to CONFIG_NET_CONFIG_*.

Prior to this commit a function compiled with the native decorator
@micropython.native would not work correctly when accessing global
variables, because the globals dict was not being set upon function entry.

This commit fixes this problem by, upon function entry, setting as the
current globals dict the globals dict context the function was defined
within, as per normal Python semantics, and as bytecode does.  Upon
function exit the original globals dict is restored.

In order to restore the globals dict when an exception is raised the native
function must guard its internals with an nlr_push/nlr_pop pair.  Because
this push/pop is relatively expensive, in both C stack usage for the
nlr_buf_t and CPU execution time, the implementation here optimises things
as much as possible.  First, the compiler keeps track of whether a function
even needs to access global variables.  Using this information the native
emitter then generates three different kinds of code:

1. no globals used, no exception handlers: no nlr handling code and no
   setting of the globals dict.

2. globals used, no exception handlers: an nlr_buf_t is allocated on the
   C stack but it is not used if the globals dict is unchanged, saving
   execution time because nlr_push/nlr_pop don't need to run.

3. function has exception handlers, may use globals: an nlr_buf_t is
   allocated and nlr_push/nlr_pop are always called.

In the end, native functions that don't access globals and don't have
exception handlers will run more efficiently than those that do.

Fixes issue #1573.