xcb-util-wm: add m4 build system dependency (#11056)

var/spack/repos/builtin/packages/xcb-util-wm/package.py

@@ -19,6 +19,8 @@ class XcbUtilWm(AutotoolsPackage):
 
     version('0.4.1', '0831399918359bf82930124fa9fd6a9b')
 
+    depends_on('m4',       type='build')
+
     depends_on('libxcb@1.4:')
 
     depends_on('pkgconfig', type='build')