Rename variables: r_gdt -> saved_gdt r_idt -> saved_idt r_ldt -> saved_ldt
Rename variables:
r_gdt -> saved_gdt
r_idt -> saved_idt
r_ldt -> saved_ldt

in order to prevent clashes with variables with same names
defined in <machine/segments.h>.  This fixes compilation of this
file with GCC 4.0.

Reviewed by:	njl

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