beast1: add libbeagle support (#8525)

var/spack/repos/builtin/packages/beast1/package.py

@@ -36,7 +36,10 @@ class Beast1(Package):
             url='https://github.com/beast-dev/beast-mcmc/releases/download/v1.10.0/BEAST_v1.10.0.tgz')
     version('1.8.4', 'cb8752340c1f77a22d39ca4fe09687b0')
 
+    variant('beagle', default=True, description='Build with libbeagle support')
+
     depends_on('java', type='run')
+    depends_on('libbeagle', type=('build', 'link', 'run'), when="+beagle")
 
     def setup_environment(self, spack_env, run_env):
         run_env.set('BEAST1', self.prefix)