Disable Driver/env.c on AIX (NFC) (#161874)

AIX does not use LD_LIBRARY_PATH.

Author: kkwli

clang/test/Driver/env.c

@@ -1,5 +1,7 @@
 // Some assertions in this test use Linux style (/) file paths.
-// UNSUPPORTED: system-windows
+// TODO: Use LIBPATH on AIX
+// UNSUPPORTED: system-windows, system-aix
+
 // RUN: bash -c env | grep LD_LIBRARY_PATH | sed -ne 's/^.*=//p' | tr -d '\n' > %t.ld_library_path
 // The PATH variable is heavily used when trying to find a linker.
 // RUN: env -i LC_ALL=C LD_LIBRARY_PATH="%{readfile:%t.ld_library_path}" CLANG_NO_DEFAULT_CONFIG=1 \