+#
+# 's|\\|/|g'
+# We first normalise all slashes to be forward slashes. Note that
+# $(TOP) also uses forward slashes.
+# 's| /$$| \\|'
+# But now we need to fix the line continuation characters that we
+# just broke.
+# "1s|\.o|\.$($w_osuf)|"
+# We will have dependencies for .o files, so we need to fix them up
+# for the right object suffix for the way we're doing
+# "1s|^|$(dir $4)|"
+# We always get deps for just foo.o when the file we're making is
+# a/b/c/foo.o, so we need to prepend the directory of the source file
+# "1s|$1/|$1/$2/build/|"
+# Well, almost. We actually need to insert e.g. "dist/build" in the
+# middle of that directory
+# "1s|$2/build/$2/build|$2/build|g"
+# But some source files, e.g. sm/Evac_thr.c, are also inside the
+# "dist/build" directory, so now we've just made
+# "dist/build/dist/build", so we need to remove the duplication
+# again
+# "s|$(TOP)/||g$(CASE_INSENSITIVE_SED)"
+# Finally, when making deps for packages like ghc stage2, we have
+# some include paths for packages registered in the in-tree package
+# database. These include paths are full (i.e. not relative) paths,
+# which means that the "cpp -MM" output uses full paths in some cases.
+# This causes 2 problems:
+# * they don't match up with the rules to rebuild the files, where
+# appropriate.
+# * on Windows, make interprets the colon in c:/foo/bar.h as make
+# syntax.
+# So we sed off $(TOP). Unfortunately, on Windows, the case for the
+# drive letter is sometimes different in what $(TOP) starts with, and
+# what the path in the package database starts with. We therefore
+# need to do the substitution case-insensitively on Windows. But
+# the s///i modifier isn't portable, so we set CASE_INSENSITIVE_SED
+# to "i" on Windows and "" on any other platform.