haskell.compiler.*: locales are required for build not host

The commit adding LOCALE_ARCHIVE, 8a21e02e31, cites haddock
generation which happens during the build and on the build platform.
As it turns out, the user guide also depends on locales because
sphinx tries to set a locale during execution.

This should fix cross compiling ghc from glibc to non glibc, e.g.

  x86_64-pc-linux-gnu -> aarch64-unknown-linux-musl

pkgs/development/compilers/ghc/common-hadrian.nix

@@ -36,7 +36,6 @@
 
   libiconv ? null,
   ncurses,
-  glibcLocales ? null,
 
   # GHC can be built with system libffi or a bundled one.
   libffi ? null,
@@ -549,8 +548,8 @@ stdenv.mkDerivation (
           "${buildTargetLlvmPackages.clang}/bin/${buildTargetLlvmPackages.clang.targetPrefix}clang"
       }"
     ''
-    + lib.optionalString (stdenv.hostPlatform.libc == "glibc") ''
-      export LOCALE_ARCHIVE="${glibcLocales}/lib/locale/locale-archive"
+    + lib.optionalString (stdenv.buildPlatform.libc == "glibc") ''
+      export LOCALE_ARCHIVE="${buildPackages.glibcLocales}/lib/locale/locale-archive"
     ''
     + lib.optionalString (!stdenv.hostPlatform.isDarwin) ''
       export NIX_LDFLAGS+=" -rpath $out/lib/ghc-${version}"

pkgs/development/compilers/ghc/common-make-native-bignum.nix

@@ -29,7 +29,6 @@
 
   libiconv ? null,
   ncurses,
-  glibcLocales ? null,
 
   # GHC can be built with system libffi or a bundled one.
   libffi ? null,
@@ -436,8 +435,8 @@ stdenv.mkDerivation (
       echo -n "${buildMK}" > mk/build.mk
       sed -i -e 's|-isysroot /Developer/SDKs/MacOSX10.5.sdk||' configure
     ''
-    + lib.optionalString (stdenv.hostPlatform.libc == "glibc") ''
-      export LOCALE_ARCHIVE="${glibcLocales}/lib/locale/locale-archive"
+    + lib.optionalString (stdenv.buildPlatform.libc == "glibc") ''
+      export LOCALE_ARCHIVE="${buildPackages.glibcLocales}/lib/locale/locale-archive"
     ''
     + lib.optionalString (!stdenv.hostPlatform.isDarwin) ''
       export NIX_LDFLAGS+=" -rpath $out/lib/ghc-${version}"