Default build type set back to 'Release' (#879)

* Repeats #812 that appears to have been lost in another PR

CMakeLists.txt

@@ -7,7 +7,12 @@ if (CCACHE_PROGRAM)
     set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CCACHE_PROGRAM}")
 endif ()
 
-set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "Choose the type of build, options are: Debug, Release, RelWithDebInfo")
+if (DEFINED CMAKE_BUILD_TYPE)
+    set (CMAKE_BUILD_TYPE ${CMAKE_BUILD_TYPE} CACHE STRING "Choose the type of build, options are: Debug, Release, RelWithDebInfo")
+else ()
+    set (CMAKE_BUILD_TYPE Release CACHE STRING "Choose the type of build, options are: Debug, Release, RelWithDebInfo")
+endif ()
+
 set(CMAKE_CONFIGURATION_TYPES Debug RelWithDebInfo Release CACHE TYPE INTERNAL)
 set(ARCH native CACHE STRING "CPU to build for: -march value or native")