Fixes for GCC warnings when building with --enable-kdb

[Marin Ramesa]

These are the fixes for GCC warnings when building with --enable-kdb. 
I did not fix all warnings, some are left.

[PATCH 01/19] ddb: fix implicit declaration of functions
[PATCH 02/19] ddb/db_break.c: quiet GCC warning about uninitialized variable
[PATCH 03/19] Fix call of function with qualified void return type
[PATCH 04/19] ddb/db_examine.c: fix signedness
[PATCH 05/19] ddb/db_expr.h: remove (db_addr_t *) argument name
[PATCH 06/19] ddb: fix implicit declaration of function
[PATCH 07/19] ddb/db_run.c: remove set but unused variable
[PATCH 08/19] ddb/db_run.c: trivial stylistic fix for consistency
[PATCH 09/19] ddb/db_run.c: move declaration of brpc into SOFTWARE_SSTEP
[PATCH 10/19] ddb/db_sym.c: add parentheses around assignment used as truth 
value
[PATCH 11/19] ddb/db_variables.c: fix initializations from incompatible pointer 
type
[PATCH 12/19] ipc/ipc_print.h: include ipc/ipc_pset.h for ipc_pset_t
[PATCH 13/19] kern/startup.c: fix implicit declaration of function
[PATCH 14/19] kern/xpr.c: quiet warning about uninitialized variable
[PATCH 15/19] device/net_io.c: quiet the warning about uninitialized variable
[PATCH 16/19] Fix implicit declaration of function
[PATCH 17/19] i386/i386at/kd.c: add forward declaration
[PATCH 18/19] i386/i386/db_interface.c: add forward declaration
[PATCH 19/19] i386/i386/db_interface.c: fix implicit declaration of function