This patch fixes a bug introduced by fix to AArch64 pointer tagging.
In our fix for tagged pointer support our agreed approach was to sign
extend user-space address after clearing tag bits. This is not same
for all architectures and this patch allows sign extension for
addresses on targets which specifically set significant_addr_bit.
More information about patch that caused the issues and discussion
around tagged pointer support can be found in links below:
PR gdb/23210
* gdbarch.sh (significant_addr_bit): Default to zero when
not set by target architecture.
* gdbarch.c: Re-generated.
* utils.c (address_significant): Update.