ghc: don’t add libiconv automatically

ghc needs it to fail to correctly detect it for later.

pkgs/development/libraries/gettext/gettext-setup-hook.sh

@@ -10,7 +10,7 @@ addEnvHooks "$hostOffset" gettextDataDirsHook
 
 # libintl must be listed in load flags on non-Glibc
 # it doesn't hurt to have it in Glibc either though
-if [ ! -z "@gettextNeedsLdflags@" ]; then
+if [ -n "@gettextNeedsLdflags@" -a -z "$dontAddExtraLibs" ]; then
     # See pkgs/build-support/setup-hooks/role.bash
     getHostRole
     export NIX_${role_pre}LDFLAGS+=" -lintl"

pkgs/development/libraries/libiconv/setup-hook.sh

@@ -2,5 +2,7 @@
 # it doesn't hurt to have it in Glibc either though
 
 # See pkgs/build-support/setup-hooks/role.bash
-getHostRole
-export NIX_${role_pre}LDFLAGS+=" -liconv"
+if [ -z "$dontAddExtraLibs" ]; then
+    getHostRole
+    export NIX_${role_pre}LDFLAGS+=" -liconv"
+fi