From: "Nakajima, Jun" <jun.nakajima@intel.com>

Split the increasingly messy compiler.h file into per-compiler files and also
add support for non-gcc compilers.  

With the current implementation:

  include/linux/compiler.h defines the compiler-dependent abstractions
  which can be overwritten by per-compiler definitions.

  include/linux/compiler-gcc.h contains the common definitions for all gcc
  versions.

  include/linux/compiler-gcc[2,3,+].h contains gcc major version specific
  definitions.

  include/linux/compiler-intel.h contains intel compiler specific
  definitions."