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/dealii/package.py

@@ -71,6 +71,9 @@ class Dealii(CMakePackage):
             description='Compile with 64 bit indices support')
     variant('optflags', default=False,
             description='Compile using additional optimization flags')
+    variant('build_type', default='DebugRelease',
+            description='The build type to build',
+            values=('Debug', 'Release', 'DebugRelease'))
 
     # required dependencies, light version
     depends_on("blas")
@@ -136,10 +139,6 @@ class Dealii(CMakePackage):
               '+slepc', '+trilinos']:
         conflicts(p, when='~mpi')
 
-    def build_type(self):
-        # CMAKE_BUILD_TYPE should be DebugRelease | Debug | Release
-        return 'DebugRelease'
-
     def cmake_args(self):
         spec = self.spec
         options = []