gnunet-fuse: Fix compile with glibc

gnunet-fuse: Fix compile with glibc

Always use pthread_mutexattr_settype() the
pthread_mutexattr_setkind_np() function is not available in the
glibc and musl version used by OpenWrt.

This fixes the following compile error:
arc-openwrt-linux-gnu/bin/ld: gnunet_fuse-mutex.o: in function `GNUNET_mutex_create':
mutex.c:(.text+0x14): undefined reference to `pthread_mutexattr_setkind_np'
arc-openwrt-linux-gnu/bin/ld: mutex.c:(.text+0x14): undefined reference to `pthread_mutexattr_setkind_np'
arc-openwrt-linux-gnu/bin/ld: mutex.c:(.text+0x76): undefined reference to `pthread_mutexattr_setkind_np'
arc-openwrt-linux-gnu/bin/ld: mutex.c:(.text+0x76): undefined reference to `pthread_mutexattr_setkind_np'
collect2: error: ld returned 1 exit status

This patch was taken from:
https://aur.archlinux.org/cgit/aur.git/plain/pthread_mutexattr_settype.patch?h=gnunet-fuse

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>