Make hppa-hpux-nat.c:hppa_hpux_save_state_offset static.

Make hppa-hpux-nat.c:hppa_hpux_save_state_offset static.

Dave reports:

> There is one small (...) issue that needs fixing:
>
> gcc -g -O2   -I. -I../../src/gdb -I../../src/gdb/common -I../../src/gdb/config -DLOCALEDIR="\"/opt/gnu64/share/locale\"" -DHAVE_CONFIG_H -I../../src/gdb/../include/opcode -I../../src/gdb/../opcodes/.. -I../../src/gdb/../readline/.. -I../bfd -I../../src/gdb/../bfd -I../../src/gdb/../include -I../libdecnumber -I../../src/gdb/../libdecnumber  -I../../src/gdb/gnulib/import -Ibuild-gnulib/import   -DTUI=1  -Wall -Wdeclaration-after-statement -Wpointer-arith -Wformat-nonliteral -Wno-pointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wmissing-prototypes -Wdeclaration-after-statement -Wempty-body -Werror -c -o hppa-hpux-nat.o -MT hppa-hpux-nat.o -MMD -MP -MF .deps/hppa-hpux-nat.Tpo ../../src/gdb/hppa-hpux-nat.c
> ../../src/gdb/hppa-hpux-nat.c:45:1: error: no previous prototype for 'hppa_hpux_save_state_offset' [-Werror=missing-prototypes]
> cc1: all warnings being treated as errors
>
> Believe the function should be static.

gdb/
2013-03-13  Pedro Alves  <palves@redhat.com>

	* hppa-hpux-nat.c (hppa_hpux_save_state_offset): Make static.