configure: drop macro 'AC_HEADER_TIME'

configure: drop macro 'AC_HEADER_TIME'

The macro AC_HEADER_TIME has been obsoleted by autoconf 2.70.

Not all systems provide 'sys/time.h', plus some old system didn't
allowed to include both 'time.h' and 'sys/time.h' because 'time.h'
was included by 'sys/time.h' and was not properly protected to
allow multiple inclusion.
The macro AC_HEADER_TIME helps to detect such odd case.
Nowadays all the systems properly protect 'time.h', so its safe to
unconditionally include 'time.h', even if it is also included by
'sys/time.h'.

The case of systems without 'sys/time.h' is already covered by
configure.ac through the directive
	AC_CHECK_HEADERS([sys/time.h])

Remove the obsoleted autoconf macro and simplify the code by
including 'time.h' unconditionally and check HAVE_SYS_TIME_H to
include 'sys/time.h'.

Change-Id: Iddb3f3f1d90c22668b97f8e756e1b4f733367a7d
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6010
Tested-by: jenkins
Reviewed-by: Marc Schink <dev@zapb.de>