toolchain: abstract setting -nostdinc

- newlib needs c standard includes (so no -nostdinc)
- xcc needs toolchain headers (so no -nostdinc)
- with host gcc:
  - x86_64 should not build with standard includes (-nostdinc needed)
  - native_posix should build with standard include (no -nostdinc)
..
..

To simplify, abstract this and move it to compilers/toolchains and still
depend on what the application wants.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

CMakeLists.txt

@@ -187,9 +187,8 @@ if(NOT CONFIG_RTTI)
   )
 endif()
 
-if(NOT CONFIG_NATIVE_APPLICATION)
-  set(NOSTDINC_F -nostdinc)
-endif()
+# @Intent: Obtain compiler specific flags for standard C includes
+toolchain_cc_nostdinc()
 
 zephyr_compile_options(
   -g # TODO: build configuration enough?
@@ -201,7 +200,6 @@ zephyr_compile_options(
   -ffreestanding
   -Wno-main
   -fno-common
-  ${NOSTDINC_F}
   ${TOOLCHAIN_C_FLAGS}
 )
 
@@ -478,7 +476,6 @@ function(construct_add_custom_command_for_linker_pass linker_output_name output_
     ${linker_script_dep}
     COMMAND ${CMAKE_C_COMPILER}
     -x assembler-with-cpp
-    ${NOSTDINC_F}
     ${NOSYSDEF_CFLAG}
     -MD -MF ${linker_cmd_file_name}.dep -MT ${base_name}/${linker_cmd_file_name}
     ${current_includes}

cmake/compiler/gcc/target.cmake

@@ -135,3 +135,4 @@ include(${ZEPHYR_BASE}/cmake/compiler/${COMPILER}/target_security_canaries.cmake
 include(${ZEPHYR_BASE}/cmake/compiler/${COMPILER}/target_optimizations.cmake)
 include(${ZEPHYR_BASE}/cmake/compiler/${COMPILER}/target_cpp.cmake)
 include(${ZEPHYR_BASE}/cmake/compiler/${COMPILER}/target_asm.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/${COMPILER}/target_baremetal.cmake)

cmake/compiler/gcc/target_baremetal.cmake

@@ -0,0 +1,10 @@
+
+macro(toolchain_cc_nostdinc)
+
+  if (NOT CONFIG_NEWLIB_LIBC AND
+    NOT COMPILER STREQUAL "xcc" AND
+    NOT CONFIG_NATIVE_APPLICATION)
+    zephyr_compile_options( -nostdinc)
+  endif()
+
+endmacro()

cmake/compiler/host-gcc/target.cmake

@@ -82,3 +82,4 @@ include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_security_canaries.cmake)
 include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_optimizations.cmake)
 include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_cpp.cmake)
 include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_asm.cmake)
+include(${ZEPHYR_BASE}/cmake/compiler/gcc/target_baremetal.cmake)

cmake/compiler/host-gcc/target_nostdinc.cmake

@@ -1,8 +0,0 @@
-
-macro(toolchain_cc_nostdinc)
-
-  zephyr_compile_options_ifndef(CONFIG_NATIVE_APPLICATION
-    -nostdinc
-  )
-
-endmacro()