CMake: Warn Unknown Build Type (#563)

Warn if a build type passed by a user is not known in project build.

```
CMake Warning at cmake/HiPACEFunctions.cmake:76 (message):
  CMAKE_BUILD_TYPE 'adsads' is not one of
  Release;Debug;MinSizeRel;RelWithDebInfo.  Is this a typo?
Call Stack (most recent call first):
  CMakeLists.txt:94 (set_default_build_type)
```

Summary:
```
  Build type: adsads (unknown type, check warning)
```

This helps if one accidentially writes `debug` instead of `Debug`,
for instance. The result of a custom type that is undefined are no
compiler (optimization/debug) flags at all...

cmake/HiPACEFunctions.cmake

@@ -72,6 +72,10 @@ macro(set_default_build_type default_build_type)
             set_property(CACHE CMAKE_BUILD_TYPE
                     PROPERTY STRINGS ${CMAKE_CONFIGURATION_TYPES})
         endif()
+        if(NOT CMAKE_BUILD_TYPE IN_LIST CMAKE_CONFIGURATION_TYPES)
+            message(WARNING "CMAKE_BUILD_TYPE '${CMAKE_BUILD_TYPE}' is not one of "
+                    "${CMAKE_CONFIGURATION_TYPES}. Is this a typo?")
+        endif()
     endif()
 endmacro()
 
@@ -219,7 +223,12 @@ function(hipace_print_summary)
         message("     python: ${CMAKE_INSTALL_PYTHONDIR}")
     endif()
     message("")
-    message("  Build type: ${CMAKE_BUILD_TYPE}")
+    set(BLD_TYPE_UNKNOWN "")
+    if(CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR AND
+       NOT CMAKE_BUILD_TYPE IN_LIST CMAKE_CONFIGURATION_TYPES)
+        set(BLD_TYPE_UNKNOWN " (unknown type, check warning)")
+    endif()
+    message("  Build type: ${CMAKE_BUILD_TYPE}${BLD_TYPE_UNKNOWN}")
     #if(BUILD_SHARED_LIBS)
     #    message("  Library: shared")
     #else()