Use built-in support for external CMake subproject for GLEW

Requires 3.7 as GLEW contains CMake project not in root directory

CMakeLists.txt

@@ -1,8 +1,4 @@
-if(WIN32)
-    set(REQUIRED_CMAKE_VERSION 3.4)
-else()
-    set(REQUIRED_CMAKE_VERSION 3.2)
-endif()
+set(REQUIRED_CMAKE_VERSION 3.7)
 
 cmake_minimum_required(VERSION ${REQUIRED_CMAKE_VERSION})
 
@@ -502,8 +498,7 @@ ExternalProject_Add(glew
     URL_MD5 ${GLEW_MD5}
     DOWNLOAD_DIR ${SDK_DOWNLOAD_DIR}
     ${GLEW_PATCHSET}
-    CONFIGURE_COMMAND ${CMAKE_COMMAND}
-        -G "${CMAKE_GENERATOR}"
+    CMAKE_ARGS
         -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
         -DBUILD_SHARED_LIBS=${BUILD_SHARED_LIBS}
         -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
@@ -512,7 +507,7 @@ ExternalProject_Add(glew
         -DCMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES_}
         -DCMAKE_INSTALL_MESSAGE=${CMAKE_INSTALL_MESSAGE}
         -DBUILD_UTILS=OFF
-        <SOURCE_DIR>/build/cmake/
+    SOURCE_SUBDIR build/cmake
     INSTALL_DIR ${SDK_INSTALL_DIR}
 )
 list(APPEND DIST_PACK_TARGETS glew)