perlfunc: document relationship between wait() and waitpid() #469

Job	Run time
Sanity: Linux -Dusethreads	10m 11s
involved_authors_debug	0s
linux i386/ubuntu (-Dusedevel)	15m 24s
macOS (big sur) xcode 13 (-Uusethreads)	14m 53s
macOS (big sur) xcode 13 (-Duseithreads -Duseshrplib)	16m 32s
cygwin	33m 20s
install	10m 11s
linux (-Uusethreads)	9m 23s
linux (-Duseshrplib -Dusequadmath -Dusecbacktrace -Dusethreads)	11m 23s
Windows mingw64	33m 13s
linux (-Duserelocatableinc)	9m 15s
minitest	3m 34s
linux (-Dcc='clang')	9m 55s
Windows msvc142	50m 55s
linux (-Dcc='g++')	9m 32s
linux (-Accflags=-DSILENT_NO_TAINT_SUPPORT)	9m 35s
ASAN (-Accflags=-DPURIFY)	21m 34s
linux (-Accflags=-DNO_TAINT_SUPPORT)	9m 16s
ASAN (-DDEBUGGING)	22m 35s
dist-modules (latest)	2m 42s
ASAN (-Dusethreads)	22m 53s
linux (-DDEBUGGING -Accflags=-DPERL_RC_STACK)	9m 36s
dist-modules (5.24)	2m 41s
dist-modules (5.10)	2m 19s
dist-modules (5.8)	2m 19s
Test dist/ modules on MacOS system perl	5m 19s
PERL_UNICODE (-Uusethreads)	8m 40s
PERL_UNICODE (-Dusethreads -Accflags=-DPURIFY -Dcc='gcc -fsanitize=address' -Dld='gcc -fsanitize=...	23m 16s
	6h 20m 26s

Provide feedback