ghc: document Stage1Only setting

pkgs/development/compilers/ghc/8.10.1.nix

@@ -62,7 +62,14 @@ let
     endif
     DYNAMIC_GHC_PROGRAMS = ${if enableShared then "YES" else "NO"}
     INTEGER_LIBRARY = ${if enableIntegerSimple then "integer-simple" else "integer-gmp"}
-  '' + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
+  ''
+    # We only need to build stage1 on most cross-compilation because
+    # we will be running the compiler on the native system. In some
+    # situations, like native Musl compilation, we need the compiler
+    # to actually link to our new Libc. The iOS simulator is a special
+    # exception because we can’t actually run simulators binaries
+    # ourselves.
+  + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
     Stage1Only = ${if (targetPlatform.system == hostPlatform.system && !targetPlatform.isiOS) then "NO" else "YES"}
     CrossCompilePrefix = ${targetPrefix}
     HADDOCK_DOCS = NO

pkgs/development/compilers/ghc/8.6.5.nix

@@ -59,7 +59,14 @@ let
     endif
     DYNAMIC_GHC_PROGRAMS = ${if enableShared then "YES" else "NO"}
     INTEGER_LIBRARY = ${if enableIntegerSimple then "integer-simple" else "integer-gmp"}
-  '' + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
+  ''
+    # We only need to build stage1 on most cross-compilation because
+    # we will be running the compiler on the native system. In some
+    # situations, like native Musl compilation, we need the compiler
+    # to actually link to our new Libc. The iOS simulator is a special
+    # exception because we can’t actually run simulators binaries
+    # ourselves.
+  + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
     Stage1Only = ${if (targetPlatform.system == hostPlatform.system && !targetPlatform.isiOS) then "NO" else "YES"}
     CrossCompilePrefix = ${targetPrefix}
     HADDOCK_DOCS = NO

pkgs/development/compilers/ghc/8.8.2.nix

@@ -59,7 +59,14 @@ let
     endif
     DYNAMIC_GHC_PROGRAMS = ${if enableShared then "YES" else "NO"}
     INTEGER_LIBRARY = ${if enableIntegerSimple then "integer-simple" else "integer-gmp"}
-  '' + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
+  ''
+    # We only need to build stage1 on most cross-compilation because
+    # we will be running the compiler on the native system. In some
+    # situations, like native Musl compilation, we need the compiler
+    # to actually link to our new Libc. The iOS simulator is a special
+    # exception because we can’t actually run simulators binaries
+    # ourselves.
+  + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
     Stage1Only = ${if (targetPlatform.system == hostPlatform.system && !targetPlatform.isiOS) then "NO" else "YES"}
     CrossCompilePrefix = ${targetPrefix}
     HADDOCK_DOCS = NO

pkgs/development/compilers/ghc/8.8.3.nix

@@ -62,7 +62,14 @@ let
     endif
     DYNAMIC_GHC_PROGRAMS = ${if enableShared then "YES" else "NO"}
     INTEGER_LIBRARY = ${if enableIntegerSimple then "integer-simple" else "integer-gmp"}
-  '' + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
+  ''
+    # We only need to build stage1 on most cross-compilation because
+    # we will be running the compiler on the native system. In some
+    # situations, like native Musl compilation, we need the compiler
+    # to actually link to our new Libc. The iOS simulator is a special
+    # exception because we can’t actually run simulators binaries
+    # ourselves.
+  + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
     Stage1Only = ${if (targetPlatform.system == hostPlatform.system && !targetPlatform.isiOS) then "NO" else "YES"}
     CrossCompilePrefix = ${targetPrefix}
     HADDOCK_DOCS = NO

pkgs/development/compilers/ghc/8.8.4.nix

@@ -62,7 +62,14 @@ let
     endif
     DYNAMIC_GHC_PROGRAMS = ${if enableShared then "YES" else "NO"}
     INTEGER_LIBRARY = ${if enableIntegerSimple then "integer-simple" else "integer-gmp"}
-  '' + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
+  ''
+    # We only need to build stage1 on most cross-compilation because
+    # we will be running the compiler on the native system. In some
+    # situations, like native Musl compilation, we need the compiler
+    # to actually link to our new Libc. The iOS simulator is a special
+    # exception because we can’t actually run simulators binaries
+    # ourselves.
+  + stdenv.lib.optionalString (targetPlatform != hostPlatform) ''
     Stage1Only = ${if (targetPlatform.system == hostPlatform.system && !targetPlatform.isiOS) then "NO" else "YES"}
     CrossCompilePrefix = ${targetPrefix}
     HADDOCK_DOCS = NO