Evil Mangler hanging while building 5.04.3-1 on RedHat 8.0, 9.0?

This problem arose for me on RedHat 8.0, and now it's doing it on RedHat 
9.0.  However, it only ever arose on the same machine (my RedHat 8.0 laptop 
has no trouble compiling GHC).  The fact that it always happens with the 
same files regardless

When compiling ghc/compiler/absCSyn/AbsCUtils.lhs in stage-1, and 
ghc/compiler/parser/Parser.hs and libraries/base/Foreign/C/Error.hs in 
stage-2 (i.e., with ghc-inplace), my machine hangs (it's not thrashing, it 
hangs: no change after an hour, no cursor blinking, no response to any 
stimuli; it even takes a few pushes of the reset button to have any effect 
some times).

(There may be other files downstream that exhibit this behavior, but I 
haven't gotten around to pushing the process past 
libraries/base/Foreign/C/Error.hs yet.)

I suspect the Evil Mangler because I can successfully compile each of these 
modules using -Onot and setting -tmpdir to be a local directory rather than 
/tmp.  This guarantees that the NCG is used (*), and so the Evil Mangler 
doesn't come into play.

I've heard of other isolated cases of this behavior, but never heard an 
explanation.  Does anyone know what's going on?  Has anyone else 
experienced this behavior?

Cheers,

Andy

(*) Why is ghc/compiler/parser/Parser.hs compiled with -fviaC set 
explicitly?  The NCG seems to cope just fine.  Is this a hangover from bad 
old days when the NCG couldn't handle Happy-generated files?

-- 
Andy Moran                                              Ph.  (503) 526 3472
Galois Connections Inc.                                 Fax. (503) 350 0833
3875 SW Hall Blvd.                                    http://www.galois.com
Beaverton, OR 97005                                        moran@xxxxxxxxxx