Implement `silent' build rules.

Implement `silent' build rules.

* automake.in (ccer): New field in the language structure.
Initialize it for all registered languages.
(verbose_var, verbose_flag, verbose_dispatch)
(silent_flag, define_verbose_var, define_verbose_tagvar)
(define_verbose_libtool): New functions.
(handle_languages, handle_programs, handle_libraries)
(handle_ltlibraries, handle_configure)
(define_compiler_variable, define_linker_variable)
(define_per_target_linker_variable): Use them where appropriate
to define variables to implement the silent output machinery.
* lib/Automake/Options.pm (_process_option_list): Accept
`silent', turning off `portability-recursive'.
* lib/am/depend2.am: Add %VERBOSE% and %SILENT% prefixes where
appropriate.
* lib/am/lex.am: Likewise.
* lib/am/library.am: Likewise.
* lib/am/ltlibrary.am: Likewise.
* lib/am/program.am: Likewise.
* lib/am/yacc.am: Likewise.
* m4/init.m4 (AM_INIT_AUTOMAKE): Substitute, but do not define,
AM_BACKSLASH.
* tests/defs.in: Unset `V', to avoid influencing inner tests.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>