compiler-intel: fix wrong compiler barrier() macro

compiler-intel: fix wrong compiler barrier() macro

Cleanup commit 73679e508201 ("compiler-intel.h: Remove duplicate
definition") removed the double definition of __memory_barrier()
intrinsics.

However, in doing so, it also removed the preceding #undef barrier by
accident, meaning, the actual barrier() macro from compiler-gcc.h with
inline asm is still in place as __GNUC__ is provided.

Subsequently, barrier() can never be defined as __memory_barrier() from
compiler.h since it already has a definition in place and if we trust
the comment in compiler-intel.h, ecc doesn't support gcc specific asm
statements.

I don't have an ecc at hand (unsure if that's still used in the field?)
and only found this by accident during code review, a revert of that
cleanup would be simplest option.

Fixes: 73679e508201 ("compiler-intel.h: Remove duplicate definition")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>
Cc: Pranith Kumar <bobby.prani@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: mancha security <mancha1@zoho.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>