A signal handler might call sigaction(). We must block all signals,
not only our signal, to prevent a race between us and the next signal
handler.
Use /* comments */ because cpp might expand macros in ! comments
though such expansion is probably harmless.
The bridge is now shorter by 2 instructions.
Linux passes the arguments in registers, but our compiler expects
arguments on the stack. Signal handlers got garbage instead of the
signal number. Some handlers, like the one in lang/m2/libm2/sigtrp.c,
need the correct signal number.
I write a "bridge" in PowerPC assembly that moves the arguments to the
stack. I put the bridge in sigaction(), so I provide a signal() that
calls sigaction(). I remove the *.c glob or wildcard from build.lua,
so linuxppc only compiles its own signal.c, not the other signal.c for
linux386 and linux68k.
My bridge uses sigprocmask(), so I also add sigprocmask(). Because
linux386 and linux68k use globs, they also get sigprocmask(). I sync
the header files so all three Linux platforms declare execve(),
sigprocmask(), and unlink(), but not remove(), because we have
remove() in <stdio.h>.
I am using sigaction.s to test some features that we recently added to
our PowerPC assembler. These are the "hi16[...]" and "lo16[...]"
syntax, and also the extended names like "beq", "cmpwi", "li", "subi".
