Fix building latest version of flex (#2401)

* Fix building latest version of flex

* Don't need when clause

* Remove perl deps, shebang too long

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

@@ -25,17 +25,16 @@
 from spack import *
 
 
-class Libtool(Package):
-    """
-    libtool -- library building part of autotools
-    """
+class Libtool(AutotoolsPackage):
+    """libtool -- library building part of autotools."""
+
     homepage = 'https://www.gnu.org/software/libtool/'
     url = 'http://ftpmirror.gnu.org/libtool/libtool-2.4.2.tar.gz'
 
     version('2.4.6', 'addf44b646ddb4e3919805aa88fa7c5e')
     version('2.4.2', 'd2f3b7d4627e69e13514a40e72a24d50')
 
-    depends_on('m4', type='build')
+    depends_on('m4@1.4.6:', type='build')
 
     def _make_executable(self, name):
         return Executable(join_path(self.prefix.bin, name))
@@ -46,8 +45,3 @@ def setup_dependent_package(self, module, dependent_spec):
         executables = ['libtoolize', 'libtool']
         for name in executables:
             setattr(module, name, self._make_executable(name))
-
-    def install(self, spec, prefix):
-        configure("--prefix=%s" % prefix)
-        make()
-        make("install")