cmake: toolchain: remove obsolete and unused macros

The macro `toolchain_cc_nostdinc` were made obsolete with PR#24851 and
are no longer invoked.

Remove the macro implementations.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>

cmake/compiler/clang/target.cmake

@@ -83,11 +83,3 @@ if(NOT "${ARCH}" STREQUAL "posix")
   string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
 
 endif()
-
-# Load toolchain_cc-family macros
-
-macro(toolchain_cc_nostdinc)
-  if(NOT "${ARCH}" STREQUAL "posix")
-    zephyr_compile_options( -nostdinc)
-  endif()
-endmacro()

cmake/compiler/icx/target.cmake

@@ -63,11 +63,6 @@ endif()
 set(CMAKE_REQUIRED_FLAGS -nostartfiles -nostdlib ${isystem_include_flags})
 string(REPLACE ";" " " CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
 
-# Load toolchain_cc-family macros
-macro(toolchain_cc_nostdinc)
-    zephyr_compile_options( -nostdinc)
-endmacro()
-
 if(CONFIG_CPP)
   list(APPEND TOOLCHAIN_C_FLAGS "-no-intel-lib=libirc")
 endif()