Fix of #11354: Function '_write_r' of ESP32's newlibc does not write the output of function 'write(STDIO_FILENO, ...)' to the UART interface. To fix this problem, module 'newlib_syscalls_default' is now used by default. Function '_write_r' of module 'newlib_syscalls_default' uses 'stdio_write' which in turn uses 'uart_write' if module 'stdio_uart' is used which is now the default case for ESP32.
The build system contains several instances of
INCLUDES += -I$(RIOTBASE)/sys/posix/include
This is bypassing the module management system, by directly accesing
headers without depending on a module. The module is the posix module.
That line is also added when one of the posix_* modules is requested.
According to the docs, the posix module provides headers only, but in
reality there is also inet.c.
This patch:
- Moves `inet.c` into `posix_inet`, leaving `posix` as a headers-only
module.
- Rename `posix` as `posix_headers` to make it clear the module only
includes headers.
- Makes `posix_*` modules depend on `posix_headers`, thus removing the
explicit `INCLUDES+=...` in `sys/Makefile.include`.
- Ocurrences of `INCLUDES+=...` are replaced by an explicit dependency
on `posix_headers`.
Xtensa newlib version requires pthread_setcancelstate as symbol. Therefore, the module pthread was always used, which in turn requires the module xtimer. The xtimer module, however, uses TIMER_DEV(0). Therefore, tests/timers failed for TIMER_DEV(0).
