Use uintptr_t instead of uint64_t for pointers in stack frames.

[jhb]

Test Plan

• used in CheriBSD with a kernel which has CHERI capabilities as pointers (so uintptr_t is 128 bits and pointers in the stack are that size, etc.)

[jhb]

In theory this would be more RV32 friendly as well, though I don't really think we need a FreeBSD/riscv32.

sys/riscv/riscv/unwind.c

54 ↗

(On Diff #75575)

Note that we are probably using a compressed instruction (c.jalr) so subtracting 4 rather than 2 is not always correct, but it's probably close enough as the intent is to get the right symbol name for tail calls where the saved RA may in fact point to the start of a different function.