Fix build failure on OS X (#7119)

When refactoring this recently I accidentally put the
dead-strip-preventer symbol (only used on OS X) in the wrong section.

compiler/nativeGen/X86/Ppr.hs

@@ -67,7 +67,8 @@ pprNatCmmDecl proc@(CmmProc top_info lbl (ListGraph blocks)) =
     Just (Statics info_lbl _) ->
       sdocWithPlatform $ \platform ->
       (if platformHasSubsectionsViaSymbols platform
-          then ppr (mkDeadStripPreventer info_lbl) <> char ':'
+          then pprSectionHeader Text $$
+               ppr (mkDeadStripPreventer info_lbl) <> char ':'
           else empty) $$
       vcat (map (pprBasicBlock top_info) blocks) $$
          -- above: Even the first block gets a label, because with branch-chain