el_runtime.h declared only __thread_create/__thread_join; the mutex and
channel seed primitives (__mutex_*, __channel_*) were defined in
el_runtime.c but never prototyped. Under Apple clang 21 (C11) the missing
prototypes became implicit-declaration errors, and the void-returning
__channel_send/__channel_close mis-typed el_val_t (long long) returns,
so any El program using runtime/channel.el failed to compile.
- add prototypes for __mutex_new/lock/unlock and all __channel_* to el_runtime.h
- make __channel_send/__channel_close return el_val_t nil so elc's
trailing-expression codegen for the void El wrappers type-checks
Additive; unbreaks native channels for every downstream El program.
bigmerge
b2aac4bf89