cmake: use sdk-ng built toolchain for x86_64

This adds the necessary bits to utilize the x86_64 toolchain
built by sdk-ng for x86_64 when toolchain variant is either
zephyr or xtools. This allows decoupling the builds from
the host toolchain.

Newlib is also available with this toolchain so remove
the Kconfig restriction on CONFIG_NEWLIB_LIBC.

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

arch/x86_64/CMakeLists.txt

@@ -11,4 +11,7 @@ add_subdirectory(core)
 
 zephyr_compile_options(${X86_64_BASE_CFLAGS} -mx32)
 
-zephyr_link_libraries(-mx32)
+zephyr_link_libraries(
+    -mx32
+    ${LINKERFLAGPREFIX},-melf32_x86_64
+)

arch/x86_64/core/CMakeLists.txt

@@ -48,6 +48,7 @@ add_custom_command(
     -T ${CMAKE_CURRENT_SOURCE_DIR}/xuk-stub32.ld
     ${CMAKE_CURRENT_BINARY_DIR}/xuk-stub32.o
     -o ${CMAKE_CURRENT_BINARY_DIR}/xuk-stub32.elf
+    ${LINKERFLAGPREFIX},-melf_i386
   COMMAND ${CMAKE_OBJCOPY} -O binary
     ${CMAKE_CURRENT_BINARY_DIR}/xuk-stub32.elf
     ${incdir}/xuk-stub32.bin
@@ -70,4 +71,5 @@ add_custom_command(
   COMMAND ${CMAKE_C_COMPILER} -m32 -T ${CMAKE_CURRENT_SOURCE_DIR}/xuk64.ld
           -Wl,--build-id=none -nostdlib -nodefaultlibs -nostartfiles
           -o ${qkernel_file} ${CMAKE_CURRENT_BINARY_DIR}/zephyr-qemu.o
+          ${LINKERFLAGPREFIX},-melf_i386
   )

boards/x86_64/qemu_x86_64/qemu_x86_64.yaml

@@ -6,5 +6,6 @@ arch: x86_64
 toolchain:
   - zephyr
   - host
+  - xtools
 testing:
   default: true

cmake/generic_toolchain.cmake

@@ -54,7 +54,7 @@ set(ZEPHYR_TOOLCHAIN_VARIANT ${ZEPHYR_TOOLCHAIN_VARIANT} CACHE STRING "Zephyr to
 assert(ZEPHYR_TOOLCHAIN_VARIANT "Zephyr toolchain variant invalid: please set the ZEPHYR_TOOLCHAIN_VARIANT-variable")
 
 # Pick host system's toolchain if we are targeting posix
-if((${ARCH} STREQUAL "posix") OR (${ARCH} STREQUAL "x86_64"))
+if(${ARCH} STREQUAL "posix")
   if(NOT "${ZEPHYR_TOOLCHAIN_VARIANT}" STREQUAL "llvm")
     set(ZEPHYR_TOOLCHAIN_VARIANT "host")
   endif()

cmake/toolchain/xtools/target.cmake

@@ -13,6 +13,7 @@ set(CROSS_COMPILE_TARGET_riscv32 riscv32-zephyr-elf)
 set(CROSS_COMPILE_TARGET_mips     mipsel-zephyr-elf)
 set(CROSS_COMPILE_TARGET_xtensa   xtensa-zephyr-elf)
 set(CROSS_COMPILE_TARGET_arc         arc-zephyr-elf)
+set(CROSS_COMPILE_TARGET_x86_64   x86_64-zephyr-elf)
 
 set(CROSS_COMPILE_TARGET ${CROSS_COMPILE_TARGET_${ARCH}})
 set(SYSROOT_TARGET       ${CROSS_COMPILE_TARGET})
@@ -29,4 +30,7 @@ if("${ARCH}" STREQUAL "xtensa")
 
   LIST(APPEND TOOLCHAIN_LIBS hal)
   LIST(APPEND LIB_INCLUDE_DIR -L${SYSROOT_DIR}/lib)
+elseif("${ARCH}" STREQUAL "x86_64")
+  list(APPEND TOOLCHAIN_C_FLAGS -mx32)
+  list(APPEND TOOLCHAIN_LD_FLAGS -mx32)
 endif()

cmake/toolchain/zephyr/0.10.1/target.cmake

@@ -13,6 +13,7 @@ set(CROSS_COMPILE_TARGET_riscv32 riscv32-zephyr-elf)
 set(CROSS_COMPILE_TARGET_mips     mipsel-zephyr-elf)
 set(CROSS_COMPILE_TARGET_xtensa   xtensa-zephyr-elf)
 set(CROSS_COMPILE_TARGET_arc         arc-zephyr-elf)
+set(CROSS_COMPILE_TARGET_x86_64   x86_64-zephyr-elf)
 
 set(CROSS_COMPILE_TARGET ${CROSS_COMPILE_TARGET_${ARCH}})
 set(SYSROOT_TARGET       ${CROSS_COMPILE_TARGET})
@@ -28,5 +29,8 @@ if("${ARCH}" STREQUAL "xtensa")
 
   LIST(APPEND TOOLCHAIN_LIBS hal)
   LIST(APPEND LIB_INCLUDE_DIR -L${SYSROOT_DIR}/lib)
+elseif("${ARCH}" STREQUAL "x86_64")
+  list(APPEND TOOLCHAIN_C_FLAGS -mx32)
+  list(APPEND TOOLCHAIN_LD_FLAGS -mx32)
 endif()
 set(SYSROOT_DIR   ${TOOLCHAIN_HOME}/${SYSROOT_TARGET}/${SYSROOT_TARGET})

lib/libc/Kconfig

@@ -11,7 +11,6 @@ depends on !NATIVE_APPLICATION
 
 config NEWLIB_LIBC
 	bool "Build with newlib c library"
-	depends on !X86_64
 	help
 	  Build with newlib library. The newlib library is expected to be
 	  part of the SDK in this case.