AIX: Fix shared library linking with CMAKE_<LANG>_COMPILER_TARGET

With Clang, `CMAKE_C_COMPILER_TARGET` adds a `--target=` flag as part of
the `<CMAKE_C_COMPILER>` placeholder, causing the flag to be passed to
our `ExportImportList` script.  Tolerate it.

Fixes: #27167

Modules/Platform/AIX/ExportImportList

@@ -23,6 +23,7 @@ while test "$#" != 0; do
     -n) no_objects='1' ;;
     -c) shift; compiler="$1" ;;
     --) shift; break ;;
+    --target=*) ;;
     -*) die "$usage" ;;
     *)  break ;;
     esac