-lm is needed on some platforms, harmless on others

CMakeLists.txt

@@ -257,7 +257,7 @@ if(NOT PACKAGE_STATIC)
 				)
 			endif(BUILD_ARM_V5)
 		else()
-			set(GO_EXTRA_LIBRARIES "-lc++")
+			set(GO_EXTRA_LIBRARIES "-lc++" "-lm")
 		endif()
 	endif(WIN32)
 
@@ -265,7 +265,7 @@ if(NOT PACKAGE_STATIC)
 		zerotier ALL
 		BYPRODUCTS ${CMAKE_BINARY_DIR}/zerotier
 		SOURCES ${go_src}
-		COMMAND ${CMAKE_COMMAND} -E env ${GOARCH} ${GOARM} CGO_ENABLED=1 CGO_CFLAGS=\"-O3\" CGO_LDFLAGS=\"$<TARGET_FILE:zt_core> $<TARGET_FILE:zt_controller> $<TARGET_FILE:zt_service_io_core> $<TARGET_FILE:zt_osdep> ${GO_EXTRA_LIBRARIES}\" ${GO} build  -mod=vendor ${GOFLAGS} -o ${CMAKE_BINARY_DIR}/${GO_EXE_NAME} ${CMAKE_SOURCE_DIR}/cmd/zerotier/zerotier.go
+		COMMAND ${CMAKE_COMMAND} -E env ${GOARCH} ${GOARM} CGO_ENABLED=1 CGO_CFLAGS=\"-O3\" CGO_LDFLAGS=\"$<TARGET_FILE:zt_core> $<TARGET_FILE:zt_controller> $<TARGET_FILE:zt_service_io_core> $<TARGET_FILE:zt_osdep> ${GO_EXTRA_LIBRARIES}\" ${GO} build -mod=vendor ${GOFLAGS} -o ${CMAKE_BINARY_DIR}/${GO_EXE_NAME} ${CMAKE_SOURCE_DIR}/cmd/zerotier/zerotier.go
 		COMMENT "Compiling Go Code..."
 	)
 	add_dependencies(zerotier zt_osdep zt_core zt_controller zt_service_io_core)