Darwin fails with errors from dsymutil

@nineonine reports stderr mismatches on Darwin due to spurious output from dsymutil:

==nofib== fem: time to run fem follows...
../../runstdtest/runstdtest ./fem -i  fem.stdin   -ghc-timing +RTS -V0 -RTS   -cachegrind 20 ;

real    0m9.410s
user    0m8.902s
sys     0m0.399s
././fem +RTS -V0 -RTS 20 < fem.stdin
expected stderr not matched by reality
--- /var/folders/8r/mh3xgy7d7fg2zrj0y_3ch3dh0000gn/T//no_stderr6870     2020-05-12 18:57:14.000000000 -0700
+++ /var/folders/8r/mh3xgy7d7fg2zrj0y_3ch3dh0000gn/T//runtest6870.2     2020-05-12 18:57:24.000000000 -0700
@@ -0,0 +1 @@
+warning: no debug symbols in executable (-arch x86_64)
make[2]: *** [runtests] Error 1
make[2]: Target `all' not remade because of errors.
Finished making all in fem: 0