CachedCMakePackage: set build type (#38502)

Fixed the cached CMake package so that the build_type field is saved
in the cached configuration file.

lib/spack/spack/build_systems/cached_cmake.py

@@ -289,6 +289,7 @@ def std_initconfig_entries(self):
             "# CMake executable path: {0}".format(self.pkg.spec["cmake"].command.path),
             "#------------------{0}\n".format("-" * 60),
             cmake_cache_path("CMAKE_PREFIX_PATH", cmake_prefix_path),
+            self.define_cmake_cache_from_variant("CMAKE_BUILD_TYPE", "build_type"),
         ]
 
     def initconfig_package_entries(self):