cmake: source dedicated linker library properties for native builds

Native builds uses system libraries per default.
Instead of handling this in each linker_libraries.cmake files, then the
check for native build is moved one level up and for native build a
dedicated linker_libraries_native.cmake is sourced.

This simplifies the linker_libraries.cmake files as they no longer need
to check for native builds.

Signed-off-by: Torsten Rasmussen <[email protected]>

cmake/linker/ld/linker_libraries.cmake

@@ -2,21 +2,17 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-# Do not specify default link libraries when targeting host (native build).
-if(NOT CONFIG_NATIVE_BUILD)
-  set_linker_property(NO_CREATE PROPERTY c_library    "-lc")
-  set_linker_property(NO_CREATE PROPERTY rt_library   "-lgcc")
-  set_linker_property(NO_CREATE PROPERTY c++_library  "-lstdc++")
-  set_linker_property(NO_CREATE PROPERTY math_library "-lm")
-  # Keeping default include dir empty. The linker will then select libraries
-  # from its default search path. The toolchain may adjust the value to a
-  # specific location, for example gcc infrastructure will set the value based
-  # on output from --print-libgcc-file-name.
-  set_linker_property(NO_CREATE PROPERTY lib_include_dir "")
-endif()
+set_linker_property(NO_CREATE PROPERTY c_library    "-lc")
+set_linker_property(NO_CREATE PROPERTY rt_library   "-lgcc")
+set_linker_property(NO_CREATE PROPERTY c++_library  "-lstdc++")
+set_linker_property(NO_CREATE PROPERTY math_library "-lm")
+# Keeping default include dir empty. The linker will then select libraries
+# from its default search path. The toolchain may adjust the value to a
+# specific location, for example gcc infrastructure will set the value based
+# on output from --print-libgcc-file-name.
+set_linker_property(NO_CREATE PROPERTY lib_include_dir "")
 
 if(CONFIG_CPP
-   AND NOT CONFIG_NATIVE_LIBRARY
    # When new link principle is fully introduced, then the below condition can
    # be removed, and instead the external module c++ should use:
    # set_property(TARGET linker PROPERTY c++_library  "<external_c++_lib>")

cmake/linker/linker_libraries_native.cmake

@@ -0,0 +1,21 @@
+# Copyright (c) 2024 Nordic Semiconductor
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# When doing native builds, then we default to host libraries.
+# No reason for loading linker libraries properties in this case, however we do
+# define link order because that allows the build system to hook in alternative
+# C library implementations, such as minimal libc or picolibc.
+
+# Empty on purpose as we default to host libraries selected by the linker.
+set_linker_property(PROPERTY c_library "")
+set_linker_property(PROPERTY rt_library "")
+set_linker_property(PROPERTY c++_library "")
+
+# Although library properties are empty per default, then we still define link
+# order as this allows to update libraries in use elsewhere.
+if(CONFIG_CPP)
+  set_property(TARGET linker PROPERTY link_order_library "c++")
+endif()
+
+set_property(TARGET linker APPEND PROPERTY link_order_library "c;rt")

cmake/linker/lld/linker_libraries.cmake

@@ -8,7 +8,6 @@ set_linker_property(NO_CREATE TARGET linker PROPERTY rt_library "")
 set_linker_property(TARGET linker PROPERTY c++_library "-lc++;-lc++abi")
 
 if(CONFIG_CPP
-   AND NOT CONFIG_NATIVE_LIBRARY
    # When new link principle is fully introduced, then the below condition can
    # be removed, and instead the external module c++ should use:
    # set_property(TARGET linker PROPERTY c++_library  "<external_c++_lib>")

cmake/target_toolchain_flags.cmake

@@ -41,4 +41,9 @@ include(${CMAKE_CURRENT_LIST_DIR}/linker/linker_libraries_template.cmake)
 # (gcc, host-gcc etc.)
 include(${TOOLCHAIN_ROOT}/cmake/compiler/${COMPILER}/compiler_flags.cmake OPTIONAL)
 include(${TOOLCHAIN_ROOT}/cmake/linker/${LINKER}/linker_flags.cmake OPTIONAL)
-include(${TOOLCHAIN_ROOT}/cmake/linker/${LINKER}/linker_libraries.cmake OPTIONAL)
+
+if(CONFIG_NATIVE_LIBRARY)
+  include(${TOOLCHAIN_ROOT}/cmake/linker/linker_libraries_native.cmake)
+else()
+  include(${TOOLCHAIN_ROOT}/cmake/linker/${LINKER}/linker_libraries.cmake OPTIONAL)
+endif()