I am trying to compile OpenWrt with 2.6 kernel from DD-Wrt for my BCM53572. Now I use OpenWrt toolchain to compile, but stuck at this point:
CMakeFiles/odhcpd.dir/src/config.c.o: In function `odhcpd_run':
/home/openwrt/barrier_breaker/staging_dir/target-mipsel_74kc+dsp2_uClibc-0.9.33.2/usr/include/libubox/blobmsg.h:(.text+0xee2): undefined reference to `pipe2'
collect2: error: ld returned 1 exit status
CMakeFiles/odhcpd.dir/build.make:263: recipe for target 'odhcpd' failed
However 'pipe2' is defined at unistd.h and config.c truely includes it, it's odd that ld complains blobmsg.h.
Could someone solve it?

P.S: I had used DD-Wrt toolchain(4.7) to compile, without this problem, but sflash found no squashfs.