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 #16201

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;