xmobar crashes with segmentation faults?

Markus Trippelsdorf on ghc-devs reports that 8.2.1-rc2 produces crashing xmobar executables.

Program received signal SIGSEGV, Segmentation fault.
 0x0000000000873aa8 in ghczmprim_GHCziClasses_eqChar_info ()

or:

 Program received signal SIGSEGV, Segmentation fault.
 0x0000000000873f98 in ghczmprim_GHCziClasses_zdfEqModulezuzdszdczeze_info ()
 (gdb) bt
 #0  0x0000000000873f98 in ghczmprim_GHCziClasses_zdfEqModulezuzdszdczeze_info ()
 #1  0x0000000000000000 in ?? ()

Edited Mar 10, 2019 by Ben Gamari

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