add types: (u)int64ptr_t

This type represents an integer value of at least 64 bits which is
capable of being cast to and from pointer types.  It is intended to
replace various spellings of (u)int64_t there the value is expected to
hold a pointer.  This is common in Linux code to allow 32-bit and 64-bit
structures to be the same and used other places including OpenZFS.  With
the introduction of CHERI this no longer works, but we need to preserve
the ABI for integer pointer targets.  Rather than adding ifdefs in every
case, we introduce a new type.

Reviewed by:	kib, markj
Effort:		CHERI upstreaming
Sponsored by:	Innovate UK
Differential Revision:	https://reviews.freebsd.org/D53823

sys/sys/_stdint.h

@@ -78,6 +78,22 @@ typedef	__intptr_t		intptr_t;
 typedef	__uintptr_t		uintptr_t;
 #define	_UINTPTR_T_DECLARED
 #endif
+#if defined(__BSD_VISIBLE) && __BSD_VISIBLE
+/*
+ * Integer types which are 64-bits unless it needs to be larger to hold
+ * a pointer.  These are to be used when the ABI for integer targets
+ * uses a fixed 64-bit integer to hold values including pointers in
+ * order to simplify 32- and 64-bit compatibility.
+ */
+#ifndef _INT64PTR_T_DECLARED
+typedef	__int64ptr_t		int64ptr_t;
+#define	_INT64PTR_T_DECLARED
+#endif
+#ifndef _UINT64PTR_T_DECLARED
+typedef	__uint64ptr_t		uint64ptr_t;
+#define	_UINT64PTR_T_DECLARED
+#endif
+#endif
 #ifndef _INTMAX_T_DECLARED
 typedef	__intmax_t		intmax_t;
 #define	_INTMAX_T_DECLARED

sys/sys/_types.h

@@ -70,18 +70,24 @@ typedef	__uint64_t	__uintmax_t;
 #ifdef __CHERI__
 typedef	__intcap_t	__intptr_t;
 typedef	__intcap_t	__intfptr_t;
+typedef	__intptr_t	__int64ptr_t;
 typedef	__uintcap_t	__uintptr_t;
 typedef	__uintcap_t	__uintfptr_t;
+typedef	__uintptr_t	__uint64ptr_t;
 #elif __SIZEOF_POINTER__ == 8
 typedef	__int64_t	__intptr_t;
 typedef	__int64_t	__intfptr_t;
+typedef	__int64_t	__int64ptr_t;
 typedef	__uint64_t	__uintptr_t;
 typedef	__uint64_t	__uintfptr_t;
+typedef	__uint64_t	__uint64ptr_t;
 #elif __SIZEOF_POINTER__ == 4
 typedef	__int32_t	__intptr_t;
 typedef	__int32_t	__intfptr_t;
+typedef	__int64_t	__int64ptr_t;
 typedef	__uint32_t	__uintptr_t;
 typedef	__uint32_t	__uintfptr_t;
+typedef	__uint64_t	__uint64ptr_t;
 #else
 #error unsupported pointer size
 #endif