Fix version check and prefix llvm backend option

Author: martin-frbg

cmake/system.cmake

@@ -368,22 +368,20 @@ if (${TARGET} STREQUAL NEOVERSEV1)
   if (${TARGET} STREQUAL ARMV9SME)
       set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -march=armv9-a+sme -O3")
 	  if (${CMAKE_SYSTEM_NAME} STREQUAL Windows AND ${CMAKE_C_COMPILER_ID} MATCHES "Clang")
-	  set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} --aarch64-stack-hazard-size=0")
+	  set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -mllvm --aarch64-stack-hazard-size=0")
 	  endif()
   endif()
   if (${TARGET} STREQUAL VORTEXM4)
       set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -march=armv8.4-a+sme -O3")
 	  if (${CMAKE_SYSTEM_NAME} STREQUAL Windows AND ${CMAKE_C_COMPILER_ID} MATCHES "Clang")
-	  set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} --aarch64-stack-hazard-size=0")
+	  set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -mllvm --aarch64-stack-hazard-size=0")
 	  endif()
   endif()
   if (${TARGET} STREQUAL A64FX)
     if (${CMAKE_C_COMPILER_ID} STREQUAL "PGI" AND NOT NO_SVE)
       set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -Msve-intrinsics -march=armv8.2-a+sve -mtune=a64fx")
     else ()
-	  set (GCC_VERSION 0.0)
-      execute_process(COMMAND ${CMAKE_C_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION)
-      if (${GCC_VERSION} VERSION_GREATER 10.4 OR ${GCC_VERSION} VERSION_EQUAL 10.4)
+	  if (CMAKE_C_COMPILER_VERSION VERSION_GREATER 10.4 OR CMAKE_C_COMPILER_VERSION VERSION_EQUAL 10.4)
         set (KERNEL_DEFINITIONS  "${KERNEL_DEFINITIONS} -march=armv8.2-a+sve -mtune=a64fx")
       else ()
         message(FATAL_ERROR "Compiler $${CMAKE_C_COMPILER} {GCC_VERSION} does not support A64FX.")