Remove the workaround for clang 3.6.2 that did not support
'cortex-m0plus'.
clang 3.8 was already supporting it according to the PR introducing the check.
clang >=3.8 is avaible since ubuntu-xenial and debian-stretch.
The current ubuntu-bionic has clang 6 and debian-buster clang 7.
This removes overwriting 'CPU_ARCH'.
Use the -gz option to compress ELF sections containing DWARF information.
This saves around 50% of disk space, without any side effects.
See https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Debugging-Options.html#Debugging-Options
for more infomation on this option.
Some platforms have an outdated toolchain that does not support -gz so
the flag is blacklisted there. Even then, the results are quite impressive.
I used @cladmi's `buildtest` branch (https://github.com/cladmi/RIOT/tree/wip/du/buildtest)
with this change and compiled the `examples/default` application:
```
$ BUILD_IN_DOCKER=1 DOCKER="sudo docker" make -C examples/default buildtest-indocker
```
The size was obtained with:
```
$ find output -name "*.bin.bindirsize" -type f -exec tail -n1 '{}' \; | cut -f 1 | awk '{s+=$1} END {printf "%.0f", s}'
```
Results:
- Vanilla: 10328112 KB (~10GB).
- with -gz: 4982788 KB (~5GB).
This was inspired by #8496.
Rational: the periph_common module is required by (most) other periph drivers
and also during startup of the CPU/MCU to run periph_init. The latter is only
required if other periph drivers are used, hence periph_common should be a
depency of periph_* modules and *not* of the CPU/MCU. This PR fixes that
by making periph_common a depency of periph_* and removing the explicit
include in the CPU/MCU implementation.
arm-gcc version from ubuntu bionic repository is not supported in RIOT.
Both when building with `gnu` and `llvm`.
arm-none-eabi-gcc --version
arm-none-eabi-gcc (15:6.3.1+svn253039-1build1) 6.3.1 20170620
So detect this version and print an error if found.
The check is done on the building machine and not on the host when building in
docker.
The error can be disabled when building with WERROR=0.
- Copied the relevant parts of mipshal.mk from the toolchain
- Cleaned up CFLAGS and more in Makefile.include
- Added empty syscalls implementation which can be used to interface
with the UHI system
- Added a note on why -std=gnu99 is necessary for this CPU presently
