cmake: only allow gold linker for posix builds

- the gold linker doesn't currently work for NuttX builds
 - NuttX skip --print-memory-usage if using the GOLD linker
 - fixes #15400

CMakeLists.txt

@@ -221,14 +221,15 @@ endif()
 
 #=============================================================================
 
-# gold linker - use if available
-include(CMakeDependentOption)
-CMAKE_DEPENDENT_OPTION(USE_LD_GOLD
+# gold linker - use if available (posix only for now)
+if(${PX4_PLATFORM} STREQUAL "posix")
+	include(CMakeDependentOption)
+	CMAKE_DEPENDENT_OPTION(USE_LD_GOLD
 			"Use GNU gold linker" ON
 			"NOT WIN32;NOT APPLE" OFF
-)
+	)
 
-if(USE_LD_GOLD)
+	if(USE_LD_GOLD)
 		execute_process(COMMAND ${CMAKE_C_COMPILER} -fuse-ld=gold -Wl,--version ERROR_QUIET OUTPUT_VARIABLE LD_VERSION)
 		if("${LD_VERSION}" MATCHES "GNU gold")
 			set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold")
@@ -236,6 +237,7 @@ if(USE_LD_GOLD)
 		else()
 			set(USE_LD_GOLD OFF)
 		endif()
+	endif()
 endif()
 
 #=============================================================================

platforms/nuttx/CMakeLists.txt

@@ -124,7 +124,6 @@ target_link_libraries(px4 PRIVATE
 	-Wl,-Map=${PX4_CONFIG}.map
 	-Wl,--warn-common
 	-Wl,--gc-sections
-	-Wl,--print-memory-usage
 
 	-Wl,--start-group
 		${nuttx_libs}
@@ -134,6 +133,10 @@ target_link_libraries(px4 PRIVATE
 	gcc
 	)
 
+if(NOT USE_LD_GOLD)
+	target_link_libraries(px4 PRIVATE -Wl,--print-memory-usage)
+endif()
+
 target_link_libraries(px4 PRIVATE ${module_libraries})
 
 if (config_romfs_root)