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

lib/spack/spack/build_systems/cmake.py

@@ -29,7 +29,7 @@
 
 import spack.build_environment
 from llnl.util.filesystem import working_dir, join_path
-from spack.directives import depends_on
+from spack.directives import depends_on, variant
 from spack.package import PackageBase, run_after
 
 
@@ -49,11 +49,6 @@ class CMakePackage(PackageBase):
         +-----------------------------------------------+--------------------+
         | **Method**                                    | **Purpose**        |
         +===============================================+====================+
-        | :py:meth:`~.CMakePackage.build_type`          | Specify the value  |
-        |                                               | for the            |
-        |                                               | CMAKE_BUILD_TYPE   |
-        |                                               | variable           |
-        +-----------------------------------------------+--------------------+
         | :py:meth:`~.CMakePackage.root_cmakelists_dir` | Location of the    |
         |                                               | root CMakeLists.txt|
         +-----------------------------------------------+--------------------+
@@ -74,15 +69,13 @@ class CMakePackage(PackageBase):
 
     build_time_test_callbacks = ['check']
 
+    # https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html
+    variant('build_type', default='RelWithDebInfo',
+            description='The build type to build',
+            values=('Debug', 'Release', 'RelWithDebInfo', 'MinSizeRel'))
+
     depends_on('cmake', type='build')
 
-    def build_type(self):
-        """Returns the correct value for the ``CMAKE_BUILD_TYPE`` variable
-
-        :return: value for ``CMAKE_BUILD_TYPE``
-        """
-        return 'RelWithDebInfo'
-
     @property
     def root_cmakelists_dir(self):
         """The relative path to the directory containing CMakeLists.txt
@@ -108,8 +101,8 @@ def std_cmake_args(self):
     def _std_args(pkg):
         """Computes the standard cmake arguments for a generic package"""
         try:
-            build_type = pkg.build_type()
-        except AttributeError:
+            build_type = pkg.spec.variants['build_type'].value
+        except KeyError:
             build_type = 'RelWithDebInfo'
 
         args = ['-DCMAKE_INSTALL_PREFIX:PATH={0}'.format(pkg.prefix),