cmake: toolchain: Introduce TOOLCHAIN_HAS_GLIBCXX

This commit introduces `TOOLCHAIN_HAS_GLIBCXX` CMake variable, which is
set to `y` when GNU C++ Standard Library aka. libstdc++ is available.

This helps filter libstdc++-specific Kconfig and tests in a more refined
manner.

Signed-off-by: Stephanos Ioannidis <[email protected]>

Author: stephanosio

cmake/modules/kconfig.cmake

@@ -129,6 +129,12 @@ else()
   set(_local_TOOLCHAIN_HAS_PICOLIBC n)
 endif()
 
+if(TOOLCHAIN_HAS_GLIBCXX)
+  set(_local_TOOLCHAIN_HAS_GLIBCXX y)
+else()
+  set(_local_TOOLCHAIN_HAS_GLIBCXX n)
+endif()
+
 # APP_DIR: Path to the main image (sysbuild) or synonym for APPLICATION_SOURCE_DIR (non-sysbuild)
 zephyr_get(APP_DIR VAR APP_DIR APPLICATION_SOURCE_DIR)
 
@@ -157,6 +163,7 @@ set(COMMON_KCONFIG_ENV_SETTINGS
   TOOLCHAIN_KCONFIG_DIR=${TOOLCHAIN_KCONFIG_DIR}
   TOOLCHAIN_HAS_NEWLIB=${_local_TOOLCHAIN_HAS_NEWLIB}
   TOOLCHAIN_HAS_PICOLIBC=${_local_TOOLCHAIN_HAS_PICOLIBC}
+  TOOLCHAIN_HAS_GLIBCXX=${_local_TOOLCHAIN_HAS_GLIBCXX}
   EDT_PICKLE=${EDT_PICKLE}
   # Export all Zephyr modules to Kconfig
   ${ZEPHYR_KCONFIG_MODULES_DIR}

cmake/toolchain/espressif/generic.cmake

@@ -54,3 +54,4 @@ if(NOT CROSS_COMPILE_TARGET)
 endif()
 
 set(TOOLCHAIN_HAS_NEWLIB ON CACHE BOOL "True if toolchain supports newlib")
+set(TOOLCHAIN_HAS_GLIBCXX ON CACHE BOOL "True if toolchain supports libstdc++")

cmake/toolchain/gnuarmemb/generic.cmake

@@ -18,6 +18,8 @@ set(SYSROOT_TARGET       arm-none-eabi)
 
 set(CROSS_COMPILE ${TOOLCHAIN_HOME}/bin/${CROSS_COMPILE_TARGET}-)
 set(SYSROOT_DIR   ${TOOLCHAIN_HOME}/${SYSROOT_TARGET})
+
 set(TOOLCHAIN_HAS_NEWLIB ON CACHE BOOL "True if toolchain supports newlib")
+set(TOOLCHAIN_HAS_GLIBCXX ON CACHE BOOL "True if toolchain supports libstdc++")
 
 message(STATUS "Found toolchain: gnuarmemb (${GNUARMEMB_TOOLCHAIN_PATH})")

cmake/toolchain/host/generic.cmake

@@ -5,5 +5,6 @@ set(LINKER ld)
 set(BINTOOLS host-gnu)
 
 set(TOOLCHAIN_HAS_NEWLIB OFF CACHE BOOL "True if toolchain supports newlib")
+set(TOOLCHAIN_HAS_GLIBCXX ON CACHE BOOL "True if toolchain supports libstdc++")
 
 message(STATUS "Found toolchain: host (gcc/ld)")

cmake/toolchain/zephyr/generic.cmake

@@ -4,4 +4,7 @@ include(${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr/generic.cmake)
 
 set(TOOLCHAIN_KCONFIG_DIR ${ZEPHYR_SDK_INSTALL_DIR}/cmake/zephyr)
 
-message(STATUS "Found toolchain: zephyr ${SDK_VERSION} (${ZEPHYR_SDK_INSTALL_DIR})")
+# Zephyr SDK < 0.17.1 does not set TOOLCHAIN_HAS_GLIBCXX
+set(TOOLCHAIN_HAS_GLIBCXX ON CACHE BOOL "True if toolchain supports libstdc++")
+
+message(STATUS "Found toolchain: zephyr-sdk-gnu ${SDK_VERSION} (${ZEPHYR_SDK_INSTALL_DIR})")

lib/cpp/Kconfig

@@ -102,7 +102,7 @@ choice LIBCPP_IMPLEMENTATION
 	prompt "C++ Standard Library Implementation"
 	default EXTERNAL_LIBCPP if REQUIRES_FULL_LIBCPP && NATIVE_BUILD
 	default LIBCXX_LIBCPP if REQUIRES_FULL_LIBCPP && "$(ZEPHYR_TOOLCHAIN_VARIANT)" = "llvm"
-	default GLIBCXX_LIBCPP if REQUIRES_FULL_LIBCPP
+	default GLIBCXX_LIBCPP if REQUIRES_FULL_LIBCPP && "$(TOOLCHAIN_HAS_GLIBCXX)" = "y"
 	default MINIMAL_LIBCPP
 
 config MINIMAL_LIBCPP
@@ -117,6 +117,7 @@ config MINIMAL_LIBCPP
 
 config GLIBCXX_LIBCPP
 	bool "GNU C++ Standard Library"
+	depends on "$(TOOLCHAIN_HAS_GLIBCXX)" = "y"
 	depends on NEWLIB_LIBC || PICOLIBC
 	select FULL_LIBCPP_SUPPORTED
 	help