arch: posix: Select at least C11 standard

Replace the global CSTD property with the CSTD kconfig option to select
at least C11 standard.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>

arch/Kconfig

@@ -144,6 +144,12 @@ config ARCH_POSIX
 	select BARRIER_OPERATIONS_BUILTIN
 	# POSIX arch based targets get their memory cleared on entry by the host OS
 	select SKIP_BSS_CLEAR
+	# Override the C standard used for compilation to C 2011
+	# This is due to some tests using _Static_assert which is a 2011 feature, but
+	# otherwise relying on compilers supporting it also when set to C99.
+	# This was in general ok, but with some host compilers and C library versions
+	# it led to problems. So we override it to 2011 for the native targets.
+	select REQUIRES_STD_C11
 	help
 	  POSIX (native) architecture
 

arch/posix/CMakeLists.txt

@@ -196,11 +196,4 @@ if(NOT ${LLVM_SANITIZERS_ARG} STREQUAL "")
   target_compile_options(native_simulator INTERFACE ${LLVM_SANITIZERS_ARG})
 endif()
 
-# Override the C standard used for compilation to C 2011
-# This is due to some tests using _Static_assert which is a 2011 feature, but
-# otherwise relying on compilers supporting it also when set to C99.
-# This was in general ok, but with some host compilers and C library versions
-# it led to problems. So we override it to 2011 for the native targets.
-set_property(GLOBAL PROPERTY CSTD c11)
-
 add_subdirectory(core)