ltp: Add additional m4 path to autoconf.

ltp: Add additional m4 path to autoconf.

The ltp code has some m4 macros that are deeper than the default depth
that the directory depth the autotools.bbclass checks. This causes some
macros to not be found and for supported features to not be enabled.

This patch adds the extra m4 path to the autoconf arguments.

(From OE-Core rev: 4d8fa4b7a02d1d53f75943607df7e8126e6dbeb8)

Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>