sys/limits.h: Add BOOL_MAX, BITINT_MAXWIDTH, and C23 feature test macro

Add BOOL_MAX and BITINT_MAXWIDTH macros for C23 compliance, and
define the __STDC_VERSION_LIMITS_H__ feature test macro now that
the header fully conforms to C23.

Reviewed by:	fuz
Approved by:	fuz (mentor)
MFC after:	1 month
Pull Request:	https://github.com/freebsd/freebsd-src/pull/2352

include/limits.h

@@ -29,8 +29,8 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _LIMITS_H_
-#define	_LIMITS_H_
+#ifndef __STDC_VERSION_LIMITS_H__
+#define __STDC_VERSION_LIMITS_H__	202311L
 
 #include <sys/cdefs.h>
 
@@ -148,4 +148,4 @@
 #include <sys/syslimits.h>
 #endif
 
-#endif /* !_LIMITS_H_ */
+#endif /* !__STDC_VERSION_LIMITS_H__ */

sys/sys/limits.h

@@ -69,6 +69,7 @@
 #endif
 
 #if __ISO_C_VISIBLE >= 2023
+#define BOOL_MAX	1		/* max value for a bool */
 #define BOOL_WIDTH	1		/* number of bits in a bool */
 
 #define CHAR_WIDTH	__CHAR_BIT	/* number of bits in a char */
@@ -86,6 +87,12 @@
 
 #define LLONG_WIDTH	__LLONG_BIT	/* number of bits in a long long */
 #define ULLONG_WIDTH	__LLONG_BIT	/* number of bits in an unsigned long long */
+
+#ifdef __BITINT_MAXWIDTH__
+#define BITINT_MAXWIDTH	__BITINT_MAXWIDTH__
+#else
+#define BITINT_MAXWIDTH	ULLONG_WIDTH
+#endif
 #endif
 
 #if __POSIX_VISIBLE || __XSI_VISIBLE

sys/sys/syslimits.h

@@ -32,7 +32,8 @@
 #ifndef _SYS_SYSLIMITS_H_
 #define _SYS_SYSLIMITS_H_
 
-#if !defined(_STANDALONE) && !defined(_KERNEL) && !defined(_LIMITS_H_) && !defined(_SYS_PARAM_H_)
+#if !defined(_STANDALONE) && !defined(_KERNEL) && \
+    !defined(__STDC_VERSION_LIMITS_H__) && !defined(_SYS_PARAM_H_)
 #warning "No user-serviceable parts inside."
 #endif