tcl package: Install sources (#8153)

The tcl package references the original sources upon install, and the tk build
requires the tcl sources. This updates the tcl package to install its sources following
the example of #4102, and also updates the tclConfig.sh file to properly reference
the installed sources (rather than the staging directory created by Spack).

var/spack/repos/builtin/packages/tcl/package.py

@@ -61,9 +61,30 @@ def install(self, spec, prefix):
         with working_dir(self.build_directory):
             make('install')
 
+            # http://wiki.tcl.tk/17463
+            if self.spec.satisfies('@8.6:'):
+                make('install-headers')
+
             # Some applications like Expect require private Tcl headers.
             make('install-private-headers')
 
+            # Copy source to install tree
+            # A user-provided install option might re-do this
+            # https://github.com/spack/spack/pull/4102/files
+            installed_src = join_path(
+                self.spec.prefix, 'share', self.name, 'src')
+            stage_src = os.path.realpath(self.stage.source_path)
+            install_tree(stage_src, installed_src)
+
+            # Replace stage dir -> installed src dir in tclConfig
+            filter_file(
+                stage_src, installed_src,
+                join_path(self.spec.prefix, 'lib', 'tclConfig.sh'))
+
+        # Don't install binaries in src/ tree
+        with working_dir(join_path(installed_src, self.configure_directory)):
+            make('clean')
+
     @run_after('install')
     def symlink_tclsh(self):
         with working_dir(self.prefix.bin):