bug#9010: sigprocmask -> pthread_sigmask for Emacs

[Paul Eggert <eggert@cs.ucla.edu>]

On 07/08/11 00:17, Eli Zaretskii wrote:
> After your patch, will there be any code in Emacs that still uses
> sigprocmask?  If not, we could just rename the w32.c sigprocmask stub
> to pthread_sigmask.  If sigprocmask will still be used, then your
> suggestion for pthread_sigmask to call sigprocmask is TRT.

There will still be some code in lib-src/emacsclient.c that uses sigprocmask,
because emacsclient is single-threaded and does not need pthread_sigmask.
pthread_sigmask sometimes needs extra libraries, such as -lpthread;
these libraries are ordinarily linked into Emacs anyway, so it's no
big deal for Emacs to call pthread_sigmask, but I'd rather not have
single-threaded apps link to -lpthread if they don't need it.

Does emacsclient run on w32 and/or msdos?  If so, those libraries
will need both pthread_sigmask and sigprocmask.  If not, they can
simply drop sigprocmask.

I should mention that pthread_sigmask's API differs from that of sigprocmask
in one minor way: if there is an error, sigprocmask sets errno whereas pthread_sigmask
returns the error number.  Emacs doesn't care about the difference, as it
never looks at the error number, so the Windows libraries needn't worry
about this detail.