The existing infrastructure for FLEX_NO_BACKUP doesn't work reliably
when two lexers are built in parallel in the same directory. We can
probably fix that, but as a short-term workaround, just don't make
the check for psqlscanslash.l.
Per buildfarm.
psqlscan.c: FLEX_NO_BACKUP=yes
psqlscanslash.c: FLEXFLAGS = -Cfe -p -p
-psqlscanslash.c: FLEX_NO_BACKUP=yes
+# Ideally we'd check this, but parallel make causes problems:
+# psqlscanslash.c: FLEX_NO_BACKUP=yes
# Latest flex causes warnings in these files.
ifeq ($(GCC),yes)