[CMake][Fuchsia] Use standard spelling for Arm baremetal targets (#101302)

It's more common to use `none` rather than `unknown` for the OS
component in Arm baremetal targets.

Author: petrhosek

clang/cmake/caches/Fuchsia-stage2.cmake

@@ -300,15 +300,15 @@ if(FUCHSIA_SDK)
   set(LLVM_RUNTIME_MULTILIB_hwasan+noexcept_TARGETS "aarch64-unknown-fuchsia;riscv64-unknown-fuchsia" CACHE STRING "")
 endif()
 
-foreach(target armv6m-unknown-eabi;armv7m-unknown-eabi;armv8m.main-unknown-eabi)
+foreach(target armv6m-none-eabi;armv7m-none-eabi;armv8m.main-none-eabi)
   list(APPEND BUILTIN_TARGETS "${target}")
   set(BUILTINS_${target}_CMAKE_SYSTEM_NAME Generic CACHE STRING "")
   set(BUILTINS_${target}_CMAKE_SYSTEM_PROCESSOR arm CACHE STRING "")
   set(BUILTINS_${target}_CMAKE_SYSROOT "" CACHE STRING "")
   set(BUILTINS_${target}_CMAKE_BUILD_TYPE MinSizeRel CACHE STRING "")
   foreach(lang C;CXX;ASM)
     set(BUILTINS_${target}_CMAKE_${lang}_local_flags "--target=${target} -mthumb")
-    if(${target} STREQUAL "armv8m.main-unknown-eabi")
+    if(${target} STREQUAL "armv8m.main-none-eabi")
       set(BUILTINS_${target}_CMAKE_${lang}_local_flags "${BUILTINS_${target}_CMAKE_${lang}_local_flags} -mfloat-abi=softfp -march=armv8m.main+fp+dsp -mcpu=cortex-m33" CACHE STRING "")
     endif()
     set(BUILTINS_${target}_CMAKE_${lang}_FLAGS "${BUILTINS_${target}_CMAKE_${lang}_local_flags}" CACHE STRING "")