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/cbtf/package.py

@@ -58,6 +58,8 @@ class Cbtf(CMakePackage):
 
     variant('runtime', default=False,
             description="build only the runtime libraries and collectors.")
+    variant('build_type', default='None', values=('None'),
+            description='CMake build type')
 
     depends_on("cmake@3.0.2:", type='build')
     depends_on("boost@1.50.0:1.59.0")
@@ -70,9 +72,6 @@ class Cbtf(CMakePackage):
 
     build_directory = 'build_cbtf'
 
-    def build_type(self):
-        return 'None'
-
     def cmake_args(self):
 
         spec = self.spec