test failure on Haiku

On Haiku (32-bit), compiling m4-1.4.18b+fixes works fine, but one of the tests
fails:
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Checking ../../checks/198.sysval
@ ../doc/m4.texi:6749: Origin of test
../../checks/198.sysval: stdout mismatch
--- m4-tmp.10743/m4-xout	2021-05-10 01:15:42.526647296 +0000
+++ m4-tmp.10743/m4-out	2021-05-10 01:15:42.504102912 +0000
@@ -1,6 +1,6 @@
 
-2304
+5376
 
 0
 
-2304
+5376
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2304 is 0x0900, whereas 5376 is 0x1500.

On this platform, the signal number 0x09 is SIGKILL, and the signal
number 0x15 is SIGKILLTHR. I can reproduce it also in the shell:
When you kill a process with signal 9, bash reports not "Killed"
but "Kill Thread", and 'echo $?' prints not 137 but 149.

Bruno