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/m4/package.py

@@ -26,8 +26,9 @@
 import sys
 
 
-class M4(Package):
+class M4(AutotoolsPackage):
     """GNU M4 is an implementation of the traditional Unix macro processor."""
+
     homepage = "https://www.gnu.org/software/m4/m4.html"
     url      = "ftp://ftp.gnu.org/gnu/m4/m4-1.4.17.tar.gz"
 
@@ -40,19 +41,19 @@ class M4(Package):
 
     depends_on('libsigsegv', when='+sigsegv')
 
-    def install(self, spec, prefix):
-        configure_args = []
-        if 'libsigsegv' in spec:
-            configure_args.append('--with-libsigsegv-prefix=%s' %
-                                  spec['libsigsegv'].prefix)
+    def configure_args(self):
+        spec = self.spec
+        args = ['--enable-c++']
+
+        if '+sigsegv' in spec:
+            args.append('--with-libsigsegv-prefix={0}'.format(
+                spec['libsigsegv'].prefix))
         else:
-            configure_args.append('--without-libsigsegv-prefix')
+            args.append('--without-libsigsegv-prefix')
 
         # http://lists.gnu.org/archive/html/bug-m4/2016-09/msg00002.html
-        if (sys.platform == "darwin") and (spec.satisfies('%gcc')) and \
-           (spec.architecture.platform_os.version == "10.12"):
-            configure_args.append('ac_cv_type_struct_sched_param=yes')
+        if (sys.platform == 'darwin') and (spec.satisfies('%gcc')) and \
+           (spec.architecture.platform_os.version == '10.12'):
+            args.append('ac_cv_type_struct_sched_param=yes')
 
-        configure("--prefix=%s" % prefix, *configure_args)
-        make()
-        make("install")
+        return args