Resolve issues with CMake versions 3.13 and earlier

CMakeLists.txt

@@ -23,8 +23,7 @@ if(${CMAKE_SOURCE_DIR} STREQUAL ${CMAKE_CURRENT_SOURCE_DIR})
 
 	include(CPack)
 	include(GNUInstallDirs)
-	install(TARGETS glm EXPORT glm)
-	install(DIRECTORY glm TYPE INCLUDE PATTERN "CMakeLists.txt" EXCLUDE)
+	install(DIRECTORY glm DESTINATION ${CMAKE_INSTALL_INCLUDEDIR} PATTERN "CMakeLists.txt" EXCLUDE)
 	install(EXPORT glm FILE glmConfig.cmake DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/glm NAMESPACE glm::)
 	include(CMakePackageConfigHelpers)
 	write_basic_package_version_file("glmConfigVersion.cmake" COMPATIBILITY AnyNewerVersion ARCH_INDEPENDENT)

glm/CMakeLists.txt

@@ -49,6 +49,8 @@ target_include_directories(glm INTERFACE
 	$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
 )
 
+install(TARGETS glm EXPORT glm)
+
 if(BUILD_STATIC_LIBS)
 add_library(glm_static STATIC ${ROOT_TEXT} ${ROOT_MD} ${ROOT_NAT}
 	${ROOT_SOURCE}    ${ROOT_INLINE}    ${ROOT_HEADER}