CMake: Only set CMAKE_BUILD_TYPE_INIT when not set

Convenience makefile now uses CMAKE_BUILD_TYPE_INIT,
this means you can change the build type of an existing build
and it won't be overwritten when running `make`.

Useful if you want to add debug info to a release build for profiling.

CMakeLists.txt

@@ -58,7 +58,9 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/build_files/cmake/Modules")
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/build_files/cmake/platform")
 
 # avoid having empty buildtype
-set(CMAKE_BUILD_TYPE_INIT "Release")
+if(NOT DEFINED CMAKE_BUILD_TYPE_INIT)
+	set(CMAKE_BUILD_TYPE_INIT "Release")
+endif()
 
 # quiet output for Makefiles, 'make -s' helps too
 # set_property(GLOBAL PROPERTY RULE_MESSAGES OFF)

GNUmakefile

@@ -104,7 +104,7 @@ endif
 CMAKE_CONFIG = cmake $(BUILD_CMAKE_ARGS) \
                      -H"$(BLENDER_DIR)" \
                      -B"$(BUILD_DIR)" \
-                     -DCMAKE_BUILD_TYPE:STRING=$(BUILD_TYPE)
+                     -DCMAKE_BUILD_TYPE_INIT:STRING=$(BUILD_TYPE)
 
 
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