makemaker.yaml: use DESTDIR to set the install root

buildstream/plugins/elements/makemaker.yaml

diff --git a/buildstream/plugins/elements/makemaker.yaml b/buildstream/plugins/elements/makemaker.yaml
index c9c4622..3a82e00 100644
--- a/buildstream/plugins/elements/makemaker.yaml
+++ b/buildstream/plugins/elements/makemaker.yaml
@@ -14,7 +14,7 @@
   # and ExtUtil::MakeMaker's documentation for more details.
   configure: |
 
-    perl Makefile.PL PREFIX=%{install-root}%{prefix}
+    perl Makefile.PL PREFIX=%{prefix} DESTDIR=%{install-root}
 
   make: make
   make-install: make install

tests/format/variables.py

diff --git a/tests/format/variables.py b/tests/format/variables.py
index a888818..17101e0 100644
--- a/tests/format/variables.py
+++ b/tests/format/variables.py
@@ -24,7 +24,7 @@
     ('distutils.bst', 'python-install',
      "python3 setup.py install --prefix \"/usr\" \\\n" +
      "--root \"/buildstream-install\""),
-    ('makemaker.bst', 'configure', "perl Makefile.PL PREFIX=/buildstream-install/usr"),
+    ('makemaker.bst', 'configure', "perl Makefile.PL PREFIX=/usr DESTDIR=/buildstream-install"),
     ('modulebuild.bst', 'configure', "perl Build.PL --prefix \"/buildstream-install/usr\""),
     ('qmake.bst', 'make-install', "make -j1 INSTALL_ROOT=\"/buildstream-install\" install"),
 ])
@@ -50,7 +50,7 @@
     ('distutils.bst', 'python-install',
      "python3 setup.py install --prefix \"/opt\" \\\n" +
      "--root \"/custom/install/root\""),
-    ('makemaker.bst', 'configure', "perl Makefile.PL PREFIX=/custom/install/root/opt"),
+    ('makemaker.bst', 'configure', "perl Makefile.PL PREFIX=/opt DESTDIR=/custom/install/root"),
     ('modulebuild.bst', 'configure', "perl Build.PL --prefix \"/custom/install/root/opt\""),
     ('qmake.bst', 'make-install', "make -j1 INSTALL_ROOT=\"/custom/install/root\" install"),
 ])