Fix some broken links (#15733)

Summary:
For links in subpackages as well.
https://phabricator.haskell.org/D5257

Test Plan: Manually verify links

Reviewers: mpickering, bgamari, osa1

Reviewed By: osa1

GHC Trac Issues: #15733

Differential Revision: https://phabricator.haskell.org/D5262

Makefile

@@ -5,8 +5,8 @@
 # This file is part of the GHC build system.
 #
 # To understand how the build system works and how to modify it, see
-#      http://hackage.haskell.org/trac/ghc/wiki/Building/Architecture
-#      http://hackage.haskell.org/trac/ghc/wiki/Building/Modifying
+#      http://ghc.haskell.org/trac/ghc/wiki/Building/Architecture
+#      http://ghc.haskell.org/trac/ghc/wiki/Building/Modifying
 #
 # -----------------------------------------------------------------------------
 

doc/ghc.mk

@@ -5,8 +5,8 @@
 # This file is part of the GHC build system.
 #
 # To understand how the build system works and how to modify it, see
-#      http://hackage.haskell.org/trac/ghc/wiki/Building/Architecture
-#      http://hackage.haskell.org/trac/ghc/wiki/Building/Modifying
+#      http://ghc.haskell.org/trac/ghc/wiki/Building/Architecture
+#      http://ghc.haskell.org/trac/ghc/wiki/Building/Modifying
 #
 # -----------------------------------------------------------------------------