lib/vsprintf.c: move sizeof(struct printf_spec) next to its definition

At the time of commit d048419311ff ("lib/vsprintf.c: expand field_width
to 24 bits"), there was no compiletime_assert/BUILD_BUG/.... variant
that could be used outside function scope. Now we have static_assert(),
so move the assertion next to the definition instead of hiding it in
some arbitrary function.

Also add the appropriate #include to avoid relying on build_bug.h being
pulled in via some arbitrary chain of includes.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Rasmus Villemoes <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Luc Van Oostenryck <[e-mail]>
Cc: Masahiro Yamada <[e-mail]>
Cc: Nick Desaulniers <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/vsprintf.c

···
  */
 
 #include <stdarg.h>
+#include <linux/build_bug.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/module.h>	/* for KSYM_SYMBOL_LEN */
···
 	unsigned int	base:8;		/* number base, 8, 10 or 16 only */
 	signed int	precision:16;	/* # of digits/chars */
 } __packed;
+static_assert(sizeof(struct printf_spec) == 8);
+
 #define FIELD_WIDTH_MAX ((1 << 23) - 1)
 #define PRECISION_MAX ((1 << 15) - 1)
 
···
 	bool is_zero = num == 0LL;
 	int field_width = spec.field_width;
 	int precision = spec.precision;
-
-	BUILD_BUG_ON(sizeof(struct printf_spec) != 8);
 
 	/* locase = 0 or 0x20. ORing digits or letters with 'locase'
 	 * produces same digits or (maybe lowercased) letters */