invoke.texi: Document -mzarch, -mesa, -mcpu= and -march= option for S/390 and zSeries.

invoke.texi: Document -mzarch, -mesa, -mcpu= and -march= option for S/390 and zSeries.

       	* doc/invoke.texi: Document -mzarch, -mesa, -mcpu= and -march=
	option for S/390 and zSeries.
        * config/s390/s390.c (s390_cpu, s390_cpu_string, s390_arch,
        s390_arch_string): New variables.
        (override_options): Checking for options and setting of
        appropriate target_flags, cpu and arch flags.
        * config/s390/s390.h: (processor_type): New enum.
        (TARGET_SWITCHES): New switches -mesa/zarch.
        * config/s390/s390.md: New attribute 'cpu'.

From-SVN: r60364