Drop redundant `-D__GLASGOW_HASKELL__=...` flag

In 3549c952 a `include/ghcversions.h` include
file was introduced which defines `__GLASGOW_HASKELL__` as well.

So there's no need to define it twice.

compiler/main/DriverPipeline.hs

@@ -1191,9 +1191,7 @@ runPhase (RealPhase cc_phase) input_fn dflags
                        ++ verbFlags
                        ++ [ "-S" ]
                        ++ cc_opt
-                       ++ [ "-D__GLASGOW_HASKELL__="++cProjectVersionInt
-                          , "-include", ghcVersionH
-                          ]
+                       ++ [ "-include", ghcVersionH ]
                        ++ framework_paths
                        ++ split_opt
                        ++ include_paths
@@ -2032,10 +2030,7 @@ doCpp dflags raw input_fn output_fn = do
 #endif
     -- Default CPP defines in Haskell source
     ghcVersionH <- getGhcVersionPathName dflags
-    let hsSourceCppOpts =
-          [ "-D__GLASGOW_HASKELL__="++cProjectVersionInt
-          , "-include", ghcVersionH
-          ]
+    let hsSourceCppOpts = [ "-include", ghcVersionH ]
 
     -- MIN_VERSION macros
     let uids = explicitPackages (pkgState dflags)

includes/ghc.mk

@@ -60,9 +60,7 @@ $(includes_H_VERSION) : mk/project.mk | $$(dir $$@)/.
 	@echo "#ifndef __GHCVERSION_H__"  > $@
 	@echo "#define __GHCVERSION_H__" >> $@
 	@echo >> $@
-	@echo "#ifndef __GLASGOW_HASKELL__" >> $@
-	@echo "# define __GLASGOW_HASKELL__ $(ProjectVersionInt)" >> $@
-	@echo "#endif" >> $@
+	@echo "#define __GLASGOW_HASKELL__ $(ProjectVersionInt)" >> $@
 	@echo >> $@
 	@if [ -n "$(ProjectPatchLevel1)" ]; then \
 	  echo "#define __GLASGOW_HASKELL_PATCHLEVEL1__ $(ProjectPatchLevel1)" >> $@; \