* configure.ac (DEBUGDIR_RELOCATABLE): Define for debugdir inside

	* configure.ac (DEBUGDIR_RELOCATABLE): Define for debugdir inside
	exec_prefix.
	(TARGET_SYSTEM_ROOT_RELOCATABLE): Allow for exec_prefix being
	'${prefix}'.
	* configure, config.in: Regenerate.
	* defs.h (debug_file_directory): Declare.
	* main.c (captured_main): Canonicalize gdb_sysroot.  Assume
	TARGET_SYSTEM_ROOT is defined.  Initialize debug_file_directory and
	relocate it if DEBUGDIR_RELOCATABLE.
	* symfile.c (debug_file_directory): Make non-static.
	(find_separate_debug_file): Look for debug info for SYSROOT/PATH
	in DEBUGDIR/PATH if DEBUGDIR is inside SYSROOT.
	(_initialize_symfile): Don't initialize debug_file_directory here.