linux/modules/cpu_x86: support x64 grsec kernels
linux/modules/cpu_x86: support x64 grsec kernels

x64 grsec kernels forbid the use of get_cpu_gdt_table in modules as this
symbol is not exported.  As a workaround, only dump the current CPU gdt.

Moreover, with hidden symbols, sprint_symbol always returns an empty
string.  Handle this case in the IDT dumper.

fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared,fishilico/shared