Tidy up some build system code

rts/ghc.mk

@@ -70,8 +70,8 @@ endif
 
 # collect the -l flags that we need to link the rts dyn lib.
 rts/libs.depend : $$(ghc-pkg_INPLACE)
-	"$(ghc-pkg_INPLACE)" field rts extra-libraries \
-	  | sed -e 's/^extra-libraries: //' -e 's/\([a-z0-9]*\)[ ]*/-l\1 /g' > $@
+	"$(ghc-pkg_INPLACE)" --simple-output field rts extra-libraries \
+	  | -e 's/\([a-z0-9]\+\)/-l\1/g' > $@
 
 
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