include/linux/compiler*.h: make compiler-*.h mutually exclusive

Commit cafa0010cd ("Raise the minimum required gcc version to 4.6")
recently exposed a brittle part of the build for supporting non-gcc
compilers.

Both Clang and ICC define __GNUC__, __GNUC_MINOR__, and
__GNUC_PATCHLEVEL__ for quick compatibility with code bases that haven't
added compiler specific checks for __clang__ or __INTEL_COMPILER.

This is brittle, as they happened to get compatibility by posing as a
certain version of GCC.  This broke when upgrading the minimal version
of GCC required to build the kernel, to a version above what ICC and
Clang claim to be.

Rather than always including compiler-gcc.h then undefining or
redefining macros in compiler-intel.h or compiler-clang.h, let's
separate out the compiler specific macro definitions into mutually
exclusive headers, do more proper compiler detection, and keep shared
definitions in compiler_types.h.

Fixes: cafa0010cd ("Raise the minimum required gcc version to 4.6")
Reported-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Suggested-by: Eli Friedman <efriedma@codeaurora.org>
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/migrate.c

@@ -1131,7 +1131,8 @@ out:
  * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
  * around it.
  */
-#if (GCC_VERSION >= 40700 && GCC_VERSION < 40900) && defined(CONFIG_ARM)
+#if defined(CONFIG_ARM) && \
+	defined(GCC_VERSION) && GCC_VERSION < 40900 && GCC_VERSION >= 40700
 #define ICE_noinline noinline
 #else
 #define ICE_noinline