cmake(fix warning):toolchain do not have parent scope

toolchain file variable is global scope
dont need set parent scope

clear warning:
CMake Warning (dev) at /github/workspace/sources/nuttx/arch/arm/src/cmake/gcc.cmake:69 (set):
  Cannot set "GCCVER": current scope has no parent.
Call Stack (most recent call first):
  /github/workspace/sources/nuttx/arch/arm/src/cmake/Toolchain.cmake:56 (include)
  /github/workspace/sources/nuttx/build/CMakeFiles/3.26.0/CMakeSystem.cmake:6 (include)
  /github/workspace/sources/nuttx/build/CMakeFiles/CMakeScratch/TryCompile-ZJVOZO/CMakeLists.txt:5 (project)
This warning is for project developers.  Use -Wno-dev to suppress it.

Signed-off-by: xuxin19 <xuxin19@xiaomi.com>

Author: xuxin930

arch/arm/src/cmake/gcc.cmake

@@ -66,9 +66,7 @@ execute_process(COMMAND ${CMAKE_C_COMPILER} --version
                 OUTPUT_VARIABLE GCC_VERSION_OUTPUT)
 string(REGEX MATCH "\\+\\+.* ([0-9]+)\\.[0-9]+" GCC_VERSION_REGEX
              "${GCC_VERSION_OUTPUT}")
-set(GCCVER
-    ${CMAKE_MATCH_1}
-    PARENT_SCOPE)
+set(GCCVER ${CMAKE_MATCH_1})
 
 if(GCCVER EQUAL 12)
   add_compile_options(--param=min-pagesize=0)