compiler*.h: sync include/linux/compiler*.h with Linux 3.16

Copy them from Linux v3.16 tag.
My main motivation of this commit is to add compiler-clang.h.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Jeroen Hofstee <jeroen@myspectrum.nl>
diff --git a/include/linux/compiler-gcc3.h b/include/linux/compiler-gcc3.h
index 2befe65..7d89feb 100644
--- a/include/linux/compiler-gcc3.h
+++ b/include/linux/compiler-gcc3.h
@@ -2,20 +2,22 @@
 #error "Please don't include <linux/compiler-gcc3.h> directly, include <linux/compiler.h> instead."
 #endif
 
-#if __GNUC_MINOR__ >= 3
+#if GCC_VERSION < 30200
+# error Sorry, your compiler is too old - please upgrade it.
+#endif
+
+#if GCC_VERSION >= 30300
 # define __used			__attribute__((__used__))
 #else
 # define __used			__attribute__((__unused__))
 #endif
 
-#if __GNUC_MINOR__ >= 4
+#if GCC_VERSION >= 30400
 #define __must_check		__attribute__((warn_unused_result))
 #endif
 
-/*
- * A trick to suppress uninitialized variable warning without generating any
- * code
- */
-#define uninitialized_var(x) x = x
-
-#define __always_inline		inline __attribute__((always_inline))
+#ifdef CONFIG_GCOV_KERNEL
+# if GCC_VERSION < 30400
+#   error "GCOV profiling support for gcc versions below 3.4 not included"
+# endif /* __GNUC_MINOR__ */
+#endif /* CONFIG_GCOV_KERNEL */