Add universal build_type variant to CMakePackage (#4797)

* Add universal build_type variant to CMakePackage
* Override build_type in some packages with different possible values
* Remove reference to no longer existent debug variant
* Update CBTF packages with new build_type variant
* Keep note on build size of LLVM

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

@@ -46,7 +46,6 @@ class Legion(CMakePackage):
     version('develop', git='https://github.com/StanfordLegion/legion', branch='master')
     version('17.02.0', '31ac3004e2fb0996764362d2b6f6844a')
 
-    variant('debug', default=False, description='Build debug version')
     variant('mpi', default=True,
             description='Build on top of mpi conduit for mpi inoperability')
     variant('shared', default=True, description='Build shared libraries')
@@ -55,13 +54,6 @@ class Legion(CMakePackage):
     depends_on("gasnet", when='~mpi')
     depends_on("gasnet+mpi", when='+mpi')
 
-    def build_type(self):
-        spec = self.spec
-        if '+debug' in spec:
-            return 'Debug'
-        else:
-            return 'Release'
-
     def cmake_args(self):
         options = [
             '-DLegion_USE_GASNet=ON',