libupnp: mark as broken on Nios II, infamous _gp issue

libupnp: mark as broken on Nios II, infamous _gp issue

Fixes:

  http://autobuild.buildroot.org/results/bc3/bc32c15ba569e700e401ddf97faba584fc16c4cc/

The real error is in the config.log:

configure:15081: checking for UpnpInit in -lupnp
configure:15106: /home/thomas/projets/buildroot/output/host/usr/bin/nios2-linux-gnu-gcc -o conftest -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64   -Os  -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  c
onftest.c -lupnp  -lpthread -lrt  >&5
/home/thomas/projets/buildroot/output/host/opt/ext-toolchain/bin/../lib/gcc/nios2-linux-gnu/4.8.3/../../../../nios2-linux-gnu/bin/ld: /home/thomas/projets/buildroot/output/host/usr/nios2-buildroot-linux-gnu/sysroot/usr/lib/crt1.o: undefined reference to symbol '_gp'
/home/thomas/projets/buildroot/output/host/usr/nios2-buildroot-linux-gnu/sysroot/usr/lib/libthreadutil.so.6: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
configure:15106: $? = 1
[...]
configure:15125: error: libupnp not found

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>