package/libsoundtouch: needs c++

package/libsoundtouch: needs c++

Fixes
http://autobuild.buildroot.net/results/a92/a92fcb94492edfdf15c1e18c13b03d75c0210382/
http://autobuild.buildroot.net/results/d1d/d1d9a17a93f5ab61b4fbab67e0b61e79709d411f/
http://autobuild.buildroot.net/results/d55/d5548c5dbbb94bef8eccf614962d0a4fe5c91133/
http://autobuild.buildroot.net/results/798/798f103e066f94314e5664b8bcad7337e40a3fd7/
http://autobuild.buildroot.net/results/484/48407da02451382a1cf7e0c16efa7db8a338ded0/
http://autobuild.buildroot.net/results/4a0/4a0ac131884c0bc231c9f1dfd356cb533fbe5f0b/
http://autobuild.buildroot.net/results/162/1629703bc3160143875a1771f1ac25a079ec94ff/
http://autobuild.buildroot.net/results/be1/be1b69d0394de37615d3a3d2d4c4e25125b71ec2/
http://autobuild.buildroot.net/results/32b/32b9512de01af6417d2db668dc2d75953119f8ab/
http://autobuild.buildroot.net/results/1c0/1c0d433d435639f4355098fc6915c3588f922cad/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>