+# This library is linked to the compiler, at least in stage1, so we
+# better make sure it is built the same "way".
+#
+# BUT, if GhcHcOpts includes -DDEBUG we *don't* want to compile
+# lib/compat with -DDEBUG, because the preprocessor symbols used
+# by the compiler may be understood differently by library code.
+# In this particular case, it turned out that -DDEBUG made Cabal
+# import HUnit, which might not be installed for the compiler we are
+# compiling with (e.g. 6.2.1). Hence the filter-out.
+SRC_HC_OPTS += $(filter-out -D%, $(GhcHcOpts))
+
+# GHC 6.4 didn't have WCsubst.c, but 6.4.1 did, and we need to know
+# this in cbits/unicode.c The patchlevel isn't normally exposed as a
+# CPP symbol, so we have to do it by hand:
+SRC_CC_OPTS += -D__GHC_PATCHLEVEL__=$(GhcPatchLevel)