AutotoolsPackage: minor improvements (#2859)

* AutotoolsPackage: added configure_directory to permit build out of source. The configure script executable is now invoked with an absolute path. Modified a few packages accordingly.

* build_systems: functions returning directories are now properties

* build_systems: fixed issues with tcl and tk

* AutotoolsPackage: reworked recipe for autoreconf

var/spack/repos/builtin/packages/m4/package.py

@@ -41,6 +41,8 @@ class M4(AutotoolsPackage):
 
     depends_on('libsigsegv', when='+sigsegv')
 
+    build_directory = 'spack-build'
+
     def configure_args(self):
         spec = self.spec
         args = ['--enable-c++']