cmake: Toolchain abstraction: introduce toolchain_ld_cpp

No functional change expected.

This is motivated by the wish to abstract Zephyr's usage of toolchains,
permitting non-intrusive porting to other (commercial) toolchains.

Signed-off-by: Mark Ruvald Pedersen <mped@oticon.com>

CMakeLists.txt

@@ -230,9 +230,8 @@ if(NOT CONFIG_NATIVE_APPLICATION)
 endif()
 
 if(CONFIG_LIB_CPLUSPLUS)
-zephyr_ld_options(
-  -lstdc++
-)
+  # @Intent: Set linker specific flags for C++
+  toolchain_ld_cpp()
 endif()
 
 # ==========================================================================

cmake/linker/ld/target.cmake

@@ -7,3 +7,4 @@ set_ifndef(LINKERFLAGPREFIX -Wl)
 # Load toolchain_ld-family macros
 include(${ZEPHYR_BASE}/cmake/linker/${LINKER}/target_base.cmake)
 include(${ZEPHYR_BASE}/cmake/linker/${LINKER}/target_baremetal.cmake)
+include(${ZEPHYR_BASE}/cmake/linker/${LINKER}/target_cpp.cmake)

cmake/linker/ld/target_cpp.cmake

@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: Apache-2.0
+
+# See root CMakeLists.txt for description and expectations of these macros
+
+macro(toolchain_ld_cpp)
+
+  zephyr_ld_options(
+    -lstdc++
+  )
+
+endmacro()