Mapped location support
* back_end.adb (Call_Back_End): Pass information about source
files instead of units to gigi.
* gigi.h (struct File_Info_Type): New.
(gigi): Rename and change type of number_units parameter, change
type of file_info_ptr parameter.
* trans.c (number_files): New global variable.
(gigi): Rename and change type of number_units parameter, change
type of file_info_ptr parameter.
If mapped location support is enabled, create the isomorphic mapping
between source files and line maps.
(Sloc_to_locus): If mapped location support is enabled, translate
source location into mapped location.
(annotate_with_node): Rename into set_expr_location_from_node.
Call set_expr_location instead of annotate_with_locus.
(Pragma_to_gnu): Adjust for above change.
(Loop_Statement_to_gnu): Likewise.
(call_to_gnu): Likewise.
(Handled_Sequence_Of_Statements_to_gnu): Likewise.
(gnat_to_gnu): Likewise.
(add_stmt_with_node): Likewise.
(add_cleanup): Likewise.
* utils.c (gnat_init_decl_processing): Do not set input_line.