[GDB] Fix builds broken by proc-service changes.

[GDB] Fix builds broken by proc-service changes.

GLIBC BZ#20311 introduced a change to install proc_service.h so that gdb
didn't have to use the version it embeds in gdb_proc_service.h. The
embedded version is guarded by HAVE_PROC_SERVICE_H and
gdb_proc_service.h has a number other of includes and definitions, all
of which are uncondional except for an include for gregset.h. This is
only included if HAVE_PROC_SERIVCE_H is not defined.

This causes a build failure when cross compiling gdb with the latest
glibc because type definitions in gregset are used independently of
HAVE_PROC_SERIVCE_H. In particular, they are used in gdb_proc_service.h
when PRFPREGSET_T_BROKEN is set.

The error messages on the failure are
----
binutils-gdb/gdb/gdb_proc_service.h:173:9: error: ‘gdb_fpregset_t’ does
not name a type; did you mean ‘elf_fpregset_t’?
 typedef gdb_fpregset_t gdb_prfpregset_t;
         ^~~~~~~~~~~~~~
         elf_fpregset_t

binutils-gdb/gdb/gdb_proc_service.h:173:9: error: ‘gdb_fpregset_t’ does
not name a type; did you mean ‘elf_fpregset_t’?
 typedef gdb_fpregset_t gdb_prfpregset_t;
         ^~~~~~~~~~~~~~
         elf_fpregset_t

binutils-gdb/gdb/proc-service.c:218:15: error: ‘gdb_prfpregset_t’ does
not name a type; did you mean ‘gdb_fpregset_t’?
         const gdb_prfpregset_t *fpregset)
               ^~~~~~~~~~~~~~~~
               gdb_fpregset_t
----

This patch moves the include for gregset.h to before the code guarded by
HAVE_PROC_SERIVCE_H, so that it is always included. This is enough to
fix the build.

2016-08-15  Matthew Wahab  <matthew.wahab@arm.com>

	PR gdb/20457
	* gdb_proc_service.h: Add an include of gregset.h
        [!HAVE_PROC_SERVICE_H]: Remove the include of gregset.h.