libc: newlib: Cleanup/fix setting of system include paths

When we build with newlib we don't set -nostdinc.  In that case make
sure that we leave it to the toolchain to set the system include paths.

The one exception to leaving to the toolchain to set the system include
paths is the path to the newlib headers.  Since we build
with -ffreestanding we need to make sure the newlib header path is the
before the toolchain headers. Otherwise the toolchain's 'freestanding'
headers get picked up and that causes issues (for example getting PRI*64
defined properly from inttypes.h due to __STDC_HOSTED__ being '0').

For newlib we accomplish this by having the only system header specified
by zephyr_system_include_directories() being just the newlib headers.

Note: for minlibc we leave things alone as things just happen to work as
the -I include of the libc headers takes precedence over -isystem so we
get the libc headers over the toolchain ones.  For the newlib case it
appears that setting both -I and -isystem for the same dir causes the
-I to be ignored.

Fixes zephyrproject-rtos#14310

Signed-off-by: Kumar Gala <[email protected]>

Author: galak

CMakeLists.txt

@@ -348,8 +348,6 @@ endif()
 
 zephyr_cc_option_ifdef(CONFIG_STACK_USAGE            -fstack-usage)
 
-zephyr_system_include_directories(${NOSTDINC})
-
 # Force an error when things like SYS_INIT(foo, ...) occur with a missing header.
 zephyr_cc_option(-Werror=implicit-int)
 

cmake/compiler/gcc/target_baremetal.cmake

@@ -5,6 +5,7 @@ macro(toolchain_cc_nostdinc)
     NOT COMPILER STREQUAL "xcc" AND
     NOT CONFIG_NATIVE_APPLICATION)
     zephyr_compile_options( -nostdinc)
+    zephyr_system_include_directories(${NOSTDINC})
   endif()
 
 endmacro()

lib/libc/newlib/CMakeLists.txt

@@ -7,8 +7,12 @@ zephyr_library_sources(libc-hooks.c)
 # unable to, it will be up to the user to specify LIBC_*_DIR vars to
 # point to a newlib implementation.
 
+# We need to make sure this is included before the standard system
+# header include path's since we build with -ffreestanding and need
+# our libc headers to be picked instead of the toolchain's ffreestanding
+# headers.
 if(LIBC_INCLUDE_DIR)
-  zephyr_include_directories(${LIBC_INCLUDE_DIR})
+  zephyr_system_include_directories(${LIBC_INCLUDE_DIR})
 endif()
 
 if(LIBC_LIBRARY_DIR)