cmake: Don't build AVX-512 kernels with LLVM Flang.

Author: mmuetzel

cmake/system.cmake

@@ -66,6 +66,12 @@ if ((DEFINED BINARY AND BINARY EQUAL 32) OR ("$CMAKE_SIZEOF_VOID_P}" EQUAL "4"))
 endif ()
 endif ()
 
+# Disable AVX-512 for LLVM Flang
+# FIXME: Check if this is still needed with LLVM 17 or later.
+if (X86_64 AND CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
+  set(NO_AVX512 ON)
+endif ()
+
 if (INTERFACE64)
   message(STATUS "Using 64-bit integers.")
   set(GETARCH_FLAGS	"${GETARCH_FLAGS} -DUSE64BITINT")