Fix a comment

Make expands things even in comments

rules/build-dependencies.mk

@@ -52,7 +52,7 @@ endif
 # Insert the calls to hi-rule. Basically, we look for the
 #     Foo.dyn_o Foo.o : Foo.hs
 # lines, and create corresponding hi-rule lines
-#     $(eval $(call hi-rule,Foo.dyn_hi Foo.hi : %hi: %o Foo.hs))
+#     <dollar>(eval <dollar>(call hi-rule,Foo.dyn_hi Foo.hi : %hi: %o Foo.hs))
 	sed '/hs$$$$/ p                                      ; \
 	     /hs$$$$/ s/o /hi /g                             ; \
 	     /hs$$$$/ s/:/ : %hi: %o /                       ; \