Bump to e81f17d.

restore SIGCHLD sighandler to default before spawning a program

From sigaction(2):
A child created via fork(2) inherits a copy of its parent's signal dispositions.
During an execve(2), the dispositions of handled signals are reset to the default;
the dispositions of ignored signals are left unchanged.

This refused to start directly some programs from configuring in config.h:

static Key keys[] = {
	MODKEY,                       XK_o,      spawn,          {.v = cmd } },
};

Some reported programs that didn't start were: mpv, anki, dmenu_extended.

Reported by pfx.
Initial patch suggestion by Storkman.

Ref.
https://git.suckless.org/dwm/commit/e81f17d4c196aaed6893fd4beed49991caa3e2a4.html

README.md

@@ -1,4 +1,4 @@
-This dwm 6.4 (712d663, 2023-01-28) side project has a different take on dwm patching. It uses preprocessor directives to decide whether or not to include a patch during build time. Essentially this means that this build, for better or worse, contains both the patched _and_ the original code. The aim being that you can select which patches to include and the build will contain that code and nothing more. Due to the complexity of some of the patches dwm-flexipatch has diverged from mainstream dwm by making some core patches non-optional for maintenance reasons. For the classic dwm-flexipatch build refer to branch [dwm-flexipatch-1.0](https://github.com/bakkeby/dwm-flexipatch/tree/dwm-flexipatch-1.0).
+This dwm 6.4 (e81f17d, 2023-04-09) side project has a different take on dwm patching. It uses preprocessor directives to decide whether or not to include a patch during build time. Essentially this means that this build, for better or worse, contains both the patched _and_ the original code. The aim being that you can select which patches to include and the build will contain that code and nothing more. Due to the complexity of some of the patches dwm-flexipatch has diverged from mainstream dwm by making some core patches non-optional for maintenance reasons. For the classic dwm-flexipatch build refer to branch [dwm-flexipatch-1.0](https://github.com/bakkeby/dwm-flexipatch/tree/dwm-flexipatch-1.0).
 
 For example to include the `alpha` patch then you would only need to flip this setting from 0 to 1 in [patches.h](https://github.com/bakkeby/dwm-flexipatch/blob/master/patches.def.h):
 ```c

dwm.c

@@ -3985,6 +3985,8 @@ void
 spawn(const Arg *arg)
 #endif // RIODRAW_PATCH
 {
+	struct sigaction sa;
+
 	#if RIODRAW_PATCH
 	pid_t pid;
 	#endif // RIODRAW_PATCH
@@ -4050,6 +4052,12 @@ spawn(const Arg *arg)
 		}
 		#endif // SPAWNCMD_PATCH
 		setsid();
+
+		sigemptyset(&sa.sa_mask);
+		sa.sa_flags = 0;
+		sa.sa_handler = SIG_DFL;
+		sigaction(SIGCHLD, &sa, NULL);
+
 		execvp(((char **)arg->v)[0], (char **)arg->v);
 		die("dwm: execvp '%s' failed:", ((char **)arg->v)[0]);
 	}