Issue title: Compile error on brcm2708(raspberrypi) SDK
 Issue body: error log:

```shell
someone@Miku:~/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115$ make package/shadowsocks-libev/compile V=99
#
# configuration written to .config
#
make[1]: Entering directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115'
make[2]: Entering directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/package/shadowsocks-libev'
CFLAGS="-Os -pipe -march=armv6 -mtune=arm1176jzf-s -mfpu=vfp -fno-caller-saves -fhonour-copts -Wno-error=unused-but-set-variable -mfloat-abi=soft  -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/usr/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/usr/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/include " CXXFLAGS="-Os -pipe -march=armv6 -mtune=arm1176jzf-s -mfpu=vfp -fno-caller-saves -fhonour-copts -Wno-error=unused-but-set-variable -mfloat-abi=soft  -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/usr/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/usr/include -I/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/include " LDFLAGS="-L/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/usr/lib -L/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/lib -L/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/usr/lib -L/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/staging_dir/toolchain-arm_arm1176jzf-s+vfp_gcc-4.8-linaro_uClibc-116.69.203.115_eabi/lib " make   -C /home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/build_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/shadowsocks-libev/openssl/shadowsocks-libev-2.2.0/. AR=arm-openwrt-linux-uclibcgnueabi-ar AS="ccache_cc -c -Os -pipe -march=armv6 -mtune=arm1176jzf-s -mfpu=vfp -fno-caller-saves -fhonour-copts -Wno-error=unused-but-set-variable -mfloat-abi=soft" LD=arm-openwrt-linux-uclibcgnueabi-ld NM=arm-openwrt-linux-uclibcgnueabi-nm CC="ccache_cc" GCC="ccache_cc" CXX="ccache_cxx" RANLIB=arm-openwrt-linux-uclibcgnueabi-ranlib STRIP=arm-openwrt-linux-uclibcgnueabi-strip OBJCOPY=arm-openwrt-linux-uclibcgnueabi-objcopy OBJDUMP=arm-openwrt-linux-uclibcgnueabi-objdump SIZE=arm-openwrt-linux-uclibcgnueabi-size CROSS="arm-openwrt-linux-uclibcgnueabi-" ARCH="arm" ;
make[3]: Entering directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/build_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/shadowsocks-libev/openssl/shadowsocks-libev-2.2.0'
make[3]: *** No targets specified and no makefile found.  Stop.
make[3]: Leaving directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/build_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/shadowsocks-libev/openssl/shadowsocks-libev-2.2.0'
make[2]: *** [/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/build_dir/target-arm_arm1176jzf-s+vfp_uClibc-116.69.203.115_eabi/shadowsocks-libev/openssl/shadowsocks-libev-2.2.0/.built] Error 2
make[2]: Leaving directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115/package/shadowsocks-libev'
make[1]: *** [package/shadowsocks-libev/compile] Error 2
make[1]: Leaving directory `/home/someone/code/OpenWrt-SDK-brcm2708-for-linux-x86_64-gcc-4.8-linaro_uClibc-116.69.203.115'
make: *** [package/shadowsocks-libev/compile] Error 2
```

I just viewed issue #51 and linked perl in `staging_dir/host/bin/` & ```make -j 1``` but no use.
 [shadowsocks-libev](https://github.com/shadowsocks/shadowsocks-libev) could be successfuly compiled.

[barrier_breaker](http://downloads.openwrt.org/barrier_breaker/14.07/brcm2708/generic/) & [trunk](https://downloads.openwrt.org/snapshots/trunk/brcm2708/generic/) version have same error.
 Comments: 
 Comment 0: I can't reproduce the problem in the barrier_breaker.

Precompiled Download: https://drive.google.com/open?id=0B2_XcmDgxYqrSmgwcDl0Nno1dDg&authuser=0
{'source': 'GithubIssues', 'repo_name_with_owner': 'shadowsocks/openwrt-shadowsocks', 'issue_id': 74715156, 'repo_stars': 3476.0}