fix a couple misleading/wrong signal descriptions in strsignal

there are still several more that are misleading, but SIGFPE (integer
division error misdescribed as floating point) and and SIGCHLD
(possibly non-exit status change events described as exiting) were the
worst offenders.

src/string/strsignal.c

@@ -61,7 +61,7 @@ static const char strings[] =
 	"Trace/breakpoint trap\0"
 	"Aborted\0"
 	"Bus error\0"
-	"Floating point exception\0"
+	"Arithmetic exception\0"
 	"Killed\0"
 	"User defined signal 1\0"
 	"Segmentation fault\0"
@@ -70,7 +70,7 @@ static const char strings[] =
 	"Alarm clock\0"
 	"Terminated\0"
 	"Stack fault\0"
-	"Child exited\0"
+	"Child process status\0"
 	"Continued\0"
 	"Stopped (signal)\0"
 	"Stopped\0"