modified: components/libc/posix/signal/posix_signal.c Add comments to the sigqueue function, although it does not have an internal implementation
modified: components/libc/posix/signal/posix_signal.h Added detailed explanation to all members of the rt_signal_value enumeration
* [posix] POSIX standard implementation for PSE51
- add some posix's interfaces that we haven't before.
- these PR have passed the interface definition test across gcc platfrom;
- have tested base on qemu-a9 and stm32h750-art-pi.
* [newlib] only enable POSIX.1-1990
* update projects