During a full build, regmerge randomly hangs. It cannot be reproduced, but it
happens regularly (multiple times in a full build).
The only details I'm able to get are by running gdb and attaching to the stuck
process.
(gdb) bt
#0  0x4030be75 in __sigsuspend (set=0xbfffe530) at ../sysdeps/unix/sysv/linux/si
gsuspend.c:45
#1  0x401687e9 in __pthread_wait_for_restart_signal (self=0x40171f60) at pthread
.c:901
#2  0x4016aad9 in __pthread_alt_lock (lock=0x40401720, self=0x0) at restart.h:34
#3  0x40166b26 in __pthread_mutex_lock (mutex=0x40401710) at mutex.c:120
#4  0x4035ce48 in __libc_free (mem=0x80506a8) at malloc.c:3052
#5  0x401689f8 in pthread_exit_process (retcode=0, arg=0x4015dfa0) at pthread.c:
745
#6  0x4030eace in __cxa_finalize (d=0x4016dee0) at cxa_finalize.c:42
#7  0x40163fcb in __do_global_dtors_aux () from /lib/libpthread.so.0
#8  0x4016ce79 in _fini () from /lib/libpthread.so.0
#9  0x4000e4d2 in _dl_fini () at dl-fini.c:170
#10 0x4030e823 in exit (status=0) at exit.c:57
#11 0x402faf3a in __libc_start_main (main=0x8048bc8 <main>, argc=4, ubp_av=0xbff
fe8b4, init=0x8048824 <_init>, 
    fini=0x8048ea4 <_fini>, rtld_fini=0x4000e274 <_dl_fini>, stack_end=0xbfffe8a
c) at ../sysdeps/generic/libc-start.c:129

This is on Linux RH 7.0, more precisely : 
Linux homebox 2.2.16-22smp #1 SMP Tue Aug 22 16:39:21 EDT 2000 i686 unknown
(dual processor)
GNU C Library stable release version 2.2, by Roland McGrath et al.
Copyright (C) 1992-1999, 2000, 2001 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 2.96 20000731 (Red Hat Linux 7.0).
Compiled on a Linux 2.4.0-0.23smp system on 2001-01-10.
Available extensions:
        GNU libio by Per Bothner
        crypt add-on version 2.1 by Michael Glad and others
        The C stubs add-on version 2.1.2.
        BIND-8.2.3-T5B
        NIS(YP)/NIS+ NSS modules 0.19 by Thorsten Kukuk
        Glibc-2.0 compatibility add-on by Cristian Gafton 
        linuxthreads-0.9 by Xavier Leroy
        libthread_db work sponsored by Alpha Processor Inc


The stack shows that regmerge is attempting to exit, so the bug may as well be
in the Linux libc (or thread) library...