Adjust PCC bounds when calling a function by hand in AAPCS64-CAP

Adjust PCC bounds when calling a function by hand in AAPCS64-CAP

For dynamically-linked binaries using the AAPCS64-CAP ABI, the PCC bounds for
distinct DSO's can be different, and that needs to be taken into account.

Since there isn't a good interface for GDB to fetch the precise bounds (the
.plt.got could be used for this, but doesn't contain data for symbols not
being used by the program), we use maximum bounds and the existing PCC
permissions.

This allows GDB to call functions by hand in AAPCS64-CAP mode.

Also, revert a previous change to do partial writes (lower 64 bits) of the
PCC, as this isn't needed anymore.