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>

arch/arm/kernel/asm-offsets.c

@@ -38,25 +38,14 @@
 #error Sorry, your compiler targets APCS-26 but this kernel requires APCS-32
 #endif
 /*
- * GCC 3.0, 3.1: general bad code generation.
- * GCC 3.2.0: incorrect function argument offset calculation.
- * GCC 3.2.x: miscompiles NEW_AUX_ENT in fs/binfmt_elf.c
- *            (http://gcc.gnu.org/PR8896) and incorrect structure
- *	      initialisation in fs/jffs2/erase.c
  * GCC 4.8.0-4.8.2: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
  *	      miscompiles find_get_entry(), and can result in EXT3 and EXT4
  *	      filesystem corruption (possibly other FS too).
  */
-#ifdef __GNUC__
-#if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)
-#error Your compiler is too buggy; it is known to miscompile kernels.
-#error    Known good compilers: 3.3, 4.x
-#endif
-#if GCC_VERSION >= 40800 && GCC_VERSION < 40803
+#if defined(GCC_VERSION) && GCC_VERSION >= 40800 && GCC_VERSION < 40803
 #error Your compiler is too buggy; it is known to miscompile kernels
 #error and result in filesystem corruption and oopses.
 #endif
-#endif
 
 int main(void)
 {