cmake: parameterized flags to not include standard defines/files

Not all compiles/linkers support the GCC flags to not include standard
defines, include files and libraries. So make these parameters such
that the toolchain can define them when supported.

Also, according to documentation, -nostdlib does the same for both
-nostartfiles and -nodefaultlibs. So remove the redundant ones.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

CMakeLists.txt

@@ -165,8 +165,6 @@ endif()
 
 if(NOT CONFIG_NATIVE_APPLICATION)
 zephyr_ld_options(
-  -nostartfiles
-  -nodefaultlibs
   -nostdlib
   -static
   -no-pie
@@ -748,7 +746,7 @@ function(construct_add_custom_command_for_linker_pass linker_output_name output_
     COMMAND ${CMAKE_C_COMPILER}
     -x assembler-with-cpp
     ${NOSTDINC_F}
-    -undef
+    ${NOSYSDEF_CFLAG}
     -MD -MF ${linker_cmd_file_name}.dep -MT ${BASE_NAME}/${linker_cmd_file_name}
     ${ZEPHYR_INCLUDES}
     ${LINKER_SCRIPT_DEFINES}

cmake/compiler/gcc.cmake

@@ -53,6 +53,12 @@ find_program(CMAKE_CXX_COMPILER ${cplusplus_compiler} PATH ${TOOLCHAIN_HOME} NO_
 
 set(NOSTDINC "")
 
+# Note that NOSYSDEF_CFLAG may be an empty string, and
+# set_ifndef() does not work with empty string.
+if(NOT DEFINED NOSYSDEF_CFLAG)
+  set(NOSYSDEF_CFLAG -undef)
+endif()
+
 foreach(file_name include include-fixed)
   execute_process(
     COMMAND ${CMAKE_C_COMPILER} --print-file-name=${file_name}

cmake/compiler/llvm.cmake

@@ -3,6 +3,12 @@
 
 set(NOSTDINC "")
 
+# Note that NOSYSDEF_CFLAG may be an empty string, and
+# set_ifndef() does not work with empty string.
+if(NOT DEFINED NOSYSDEF_CFLAG)
+  set(NOSYSDEF_CFLAG -undef)
+endif()
+
 foreach(file_name include include-fixed)
   execute_process(
     COMMAND ${CMAKE_C_COMPILER} --print-file-name=${file_name}
@@ -19,4 +25,3 @@ endforeach()
 
 set(CMAKE_REQUIRED_FLAGS -nostartfiles -nostdlib ${isystem_include_flags} -Wl,--unresolved-symbols=ignore-in-object-files)
 string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
-

cmake/dts.cmake

@@ -92,7 +92,8 @@ if(CONFIG_HAS_DTS)
     -include ${AUTOCONF_H}
     ${DTC_INCLUDE_FLAG_FOR_DTS}  # include the DTS source and overlays
     -I${ZEPHYR_BASE}/dts/common
-    -undef -D__DTS__
+    ${NOSYSDEF_CFLAG}
+    -D__DTS__
     -P
     -E ${ZEPHYR_BASE}/misc/empty_file.c
     -o ${BOARD}.dts.pre.tmp