Linux 6.7 compat: detect if kernel defines intptr_t

Since Linux 6.7 the kernel has defined intptr_t. Clang has
-Wtypedef-redefinition by default, which causes the build to fail
because we also have a typedef for intptr_t.

Since its better to use the kernel's if it exists, detect it and skip
our own.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16201

config/kernel-types.m4

@@ -0,0 +1,40 @@
+dnl #
+dnl # check if kernel provides definitions for given types
+dnl #
+
+dnl _ZFS_AC_KERNEL_SRC_TYPE(type)
+AC_DEFUN([_ZFS_AC_KERNEL_SRC_TYPE], [
+	ZFS_LINUX_TEST_SRC([type_$1], [
+		#include <linux/types.h>
+	],[
+		const $1 __attribute__((unused)) x = ($1) 0;
+	])
+])
+
+dnl _ZFS_AC_KERNEL_TYPE(type)
+AC_DEFUN([_ZFS_AC_KERNEL_TYPE], [
+	AC_MSG_CHECKING([whether kernel defines $1])
+	ZFS_LINUX_TEST_RESULT([type_$1], [
+		AC_MSG_RESULT([yes])
+		AC_DEFINE([HAVE_KERNEL_]m4_quote(m4_translit([$1], [a-z], [A-Z])),
+		    1, [kernel defines $1])
+	], [
+		AC_MSG_RESULT([no])
+	])
+])
+
+dnl ZFS_AC_KERNEL_TYPES([types...])
+AC_DEFUN([ZFS_AC_KERNEL_TYPES], [
+	AC_DEFUN([ZFS_AC_KERNEL_SRC_TYPES], [
+		m4_foreach_w([type], [$1], [
+			_ZFS_AC_KERNEL_SRC_TYPE(type)
+		])
+	])
+	AC_DEFUN([ZFS_AC_KERNEL_TYPES], [
+		m4_foreach_w([type], [$1], [
+			_ZFS_AC_KERNEL_TYPE(type)
+		])
+	])
+])
+
+ZFS_AC_KERNEL_TYPES([intptr_t])

config/kernel.m4

@@ -37,6 +37,7 @@ dnl # only once the compilation can be done in parallel significantly
 dnl # speeding up the process.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
+	ZFS_AC_KERNEL_SRC_TYPES
 	ZFS_AC_KERNEL_SRC_OBJTOOL
 	ZFS_AC_KERNEL_SRC_GLOBAL_PAGE_STATE
 	ZFS_AC_KERNEL_SRC_ACCESS_OK_TYPE
@@ -187,6 +188,7 @@ dnl #
 dnl # Check results of kernel interface tests.
 dnl #
 AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
+	ZFS_AC_KERNEL_TYPES
 	ZFS_AC_KERNEL_ACCESS_OK_TYPE
 	ZFS_AC_KERNEL_GLOBAL_PAGE_STATE
 	ZFS_AC_KERNEL_OBJTOOL

include/os/linux/spl/sys/types.h

@@ -38,7 +38,9 @@ typedef unsigned long		ulong_t;
 typedef unsigned long long	u_longlong_t;
 typedef long long		longlong_t;
 
+#ifndef HAVE_KERNEL_INTPTR_T
 typedef long			intptr_t;
+#endif
 typedef unsigned long long	rlim64_t;
 
 typedef struct task_struct	kthread_t;