compiler.h: move __is_constexpr() to compiler.h

Prior to f747e66 __is_constexpr() was in its only user minmax.h. 
That commit moved it to const.h - but that file just defines ULL(x) and
UL(x) so that constants can be defined for .S and .c files.

So apart from the word 'const' it wasn't really a good location.  Instead
move the definition to compiler.h just before the similar

  is_signed_type() and is_unsigned_type().

This may not be a good long-term home, but the three definitions belong
together.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Laight <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Bart Van Assche <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Steven Rostedt (Google) <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: david-laight

include/linux/compiler.h

@@ -227,6 +227,14 @@ static inline void *offset_to_ptr(const int *off)
 /* &a[0] degrades to a pointer: a different type from an array */
 #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
 
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <[email protected]>
+ */
+#define __is_constexpr(x) \
+	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
 /*
  * Whether 'type' is a signed type or an unsigned type. Supports scalar types,
  * bool and also pointer types.

include/linux/const.h

@@ -3,12 +3,4 @@
 
 #include <vdso/const.h>
 
-/*
- * This returns a constant expression while determining if an argument is
- * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <[email protected]>
- */
-#define __is_constexpr(x) \
-	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
-
 #endif /* _LINUX_CONST_H */

tools/include/linux/compiler.h

@@ -63,6 +63,14 @@
 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
 #endif
 
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <[email protected]>
+ */
+#define __is_constexpr(x) \
+	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
 #ifdef __ANDROID__
 /*
  * FIXME: Big hammer to get rid of tons of:

tools/include/linux/const.h

@@ -3,12 +3,4 @@
 
 #include <vdso/const.h>
 
-/*
- * This returns a constant expression while determining if an argument is
- * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <[email protected]>
- */
-#define __is_constexpr(x) \
-	(sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
-
 #endif /* _LINUX_CONST_H */