package/pamtester: fix build without C++

pamtester uses an archaic configure.in with archaic constructs. This
had generated a configure script that incorrectly tries to look for and
validate a C++ compiler:

    checking for powerpc64le-buildroot-linux-gnu-g++... no
    checking whether we are using the GNU C++ compiler... no
    checking whether no accepts -g... no
    checking how to run the C++ preprocessor... /lib/cpp
    configure: error: C++ preprocessor "/lib/cpp" fails sanity check

Callin gautoreconf fixes the issue, as the generated configure no longer
trie to look for a C++ compiler at all anymore.

Fixes:
 - http://autobuild.buildroot.org/results/c000aff659da024b6eef42bca824bdea7b5541c2



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr: expand commit log; add big-fat comment]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>