+# Now get this: Some word that is part of the ${srcdir} directory name
+# or the ${configuration} value might, just might, happen to be an
+# identifier like `sun4' or `i386' or something, and be predefined by
+# the C preprocessor to some helpful value like 1, or maybe the empty
+# string. Needless to say consequent macro substitutions are less
+# than conducive to the makefile finding the correct directory.
+[cpp_undefs="`echo $srcdir $configuration $canonical |
+ sed -e 's/[^a-zA-Z0-9_]/ /g' -e 's/^/ /' -e 's/ *$//' \
+ -e 's/ */ -U/g' -e 's/-U[0-9][^ ]*//g'`"]
+