ltp-testsuite: disable Open POSIX testsuite

ltp-testsuite: disable Open POSIX testsuite

The Open POSIX testsuite builds and installs to the target directory a
program called 't0' that isn't cross-compiled, which is bad.

Since the LTP build system is autoconf but not automake based, and the
Open POSIX testsuite is a sort of sub-project inside it, fixing the
issue is not trivial.

Therefore, we simply disable the Open POSIX testsuite entirely. Oddly
enough, --without-open-posix-testsuite doesn't work due to another bug,
so we simply have to remove --with-open-posix-testsuite.

Open POSIX testsuite cross-compilation issue reported at
https://github.com/linux-test-project/ltp/issues/144.

Configure script bug reported at
https://github.com/linux-test-project/ltp/issues/143.

Fixes:

  http://autobuild.buildroot.net/results/8326ba9eb257dfc92c1ad282ba6d3565e8250def/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>