Add a warning to control circular dependency detection. Use "warn" as
the default action to be backward-compatible.
* src/warning.h (enum warning_type): Add warning type wt_circular_dep.
* src/warning.c (warn_init): Set default wt_circular_dep to w_warn.
* src/remake.c (update_file_1): Consult the circular-dep warning to
handle circular dependencies.
* tests/scripts/options/warn: Test --warn circular-dep flag.
* tests/scripts/variables/WARNINGS: Test .WARNINGS circular-dep flag.
* doc/make.texi: Document circular-dep warning.
* doc/make.1: Ditto.
Create a new special variable, .WARNINGS, to allow per-makefile
control over warnings. The command line settings will override
this.
Move the handling of warning flags to a new file: src/warning.c.
Allow the decode to work with generic strings, and call it from
decode_switches().
* Makefile.am: Add new file src/warning.c.
* build_w32.bat: Ditto.
* builddos.bat: Ditto.
* po/POTFILES.in: Ditto.
* src/makeint.h: #define for the .WARNINGS variable name.
* src/warning.h: Add declarations for methods moved from main.c.
Rename the enum warning_state to warning_action.
* src/warning.c: New file. Move all warning encode/decode here
from main.c.
* src/main.c: Move methods into warning.c and call those methods
instead.
(main): Set .WARNINGS as a special variable.
* src/job.c (construct_command_argv): Rename to warning_action.
* src/read.c (tilde_expand): Ditto.
* src/variable.c (set_special_var): Update warnings when the
.WARNINGS special variable is set.
* tests/scripts/options/warn: Check invalid warning options.
* tests/scripts/variables/WARNINGS: Add tests for the .WARNINGS
special variable.
