x86/uaccess: force copy_*_user() to be inlined

As already done with __copy_*_user(), mark copy_*_user() as __always_inline.
Without this, the checks for things like __builtin_const_p() won't work
consistently in either hardened usercopy nor the recent adjustments for
detecting usercopy overflows at compile time.

The change in kernel text size is detectable, but very small:

 text      data     bss     dec      hex     filename
12118735  5768608 14229504 32116847 1ea106f vmlinux.before
12120207  5768608 14229504 32118319 1ea162f vmlinux.after
Signed-off-by: Kees Cook <keescook@chromium.org>

arch/x86/include/asm/uaccess.h

@@ -705,7 +705,7 @@ static inline void copy_user_overflow(int size, unsigned long count)
 	WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
 }
 
-static inline unsigned long __must_check
+static __always_inline unsigned long __must_check
 copy_from_user(void *to, const void __user *from, unsigned long n)
 {
 	int sz = __compiletime_object_size(to);
@@ -725,7 +725,7 @@ copy_from_user(void *to, const void __user *from, unsigned long n)
 	return n;
 }
 
-static inline unsigned long __must_check
+static __always_inline unsigned long __must_check
 copy_to_user(void __user *to, const void *from, unsigned long n)
 {
 	int sz = __compiletime_object_size(from);