Avoid using an undefined cmake macro/function "build_error" (#1036)

Author: mxgrey

CHANGELOG.md

@@ -1,6 +1,10 @@
 ## DART 6
 
-### DART 6.3.1 (2018-03-14)
+### DART 6.3.1 (2018-03-21)
+
+* Build system
+
+  * Remove an undefined cmake macro/function: [#1036](https://github.com/dartsim/dart/pull/1036)
 
 * ROS support
 

CMakeLists.txt

@@ -127,7 +127,7 @@ elseif("${CMAKE_BUILD_TYPE_UPPERCASE}" STREQUAL "RELWITHDEBINFO")
 elseif("${CMAKE_BUILD_TYPE_UPPERCASE}" STREQUAL "MINSIZEREL")
   set(BUILD_TYPE_MINSIZEREL TRUE)
 else()
-  build_error("CMAKE_BUILD_TYPE ${CMAKE_BUILD_TYPE} unknown. Valid options are: Debug | Release | RelWithDebInfo | MinSizeRel")
+  message(STATUS "CMAKE_BUILD_TYPE ${CMAKE_BUILD_TYPE} unknown. Valid options are: Debug | Release | RelWithDebInfo | MinSizeRel")
 endif()
 
 #===============================================================================