Update docker/cross for new IBM toolchains

This will start using the toolchains with older glibc ABI for powerpc,
powerpc64, powerpc64le, and s390x, per rust-lang-deprecated/rust-buildbot#149.

Author: cuviper

src/ci/docker/cross/Dockerfile

@@ -1,4 +1,4 @@
-FROM alexcrichton/rust-slave-linux-cross:2016-10-11c
+FROM alexcrichton/rust-slave-linux-cross:2017-02-02
 ENTRYPOINT []
 
 ENV CARGO_TARGET_ARM_UNKNOWN_LINUX_GNUEABI_LINKER=arm-linux-gnueabi-gcc \
@@ -13,6 +13,6 @@ ENV CARGO_TARGET_ARM_UNKNOWN_LINUX_GNUEABI_LINKER=arm-linux-gnueabi-gcc \
     CARGO_TARGET_MIPS64_UNKNOWN_LINUX_GNUABI64_LINKER=mips64-linux-gnuabi64-gcc \
     CARGO_TARGET_MIPS64EL_UNKNOWN_LINUX_GNUABI64_LINKER=mips64el-linux-gnuabi64-gcc \
     CARGO_TARGET_POWERPC_UNKNOWN_LINUX_GNU_LINKER=powerpc-linux-gnu-gcc \
-    CARGO_TARGET_POWERPC64_UNKNOWN_LINUX_GNU_LINKER=powerpc64-linux-gnu-gcc-5 \
+    CARGO_TARGET_POWERPC64_UNKNOWN_LINUX_GNU_LINKER=powerpc64-linux-gnu-gcc \
     CARGO_TARGET_POWERPC64LE_UNKNOWN_LINUX_GNU_LINKER=powerpc64le-linux-gnu-gcc \
     CARGO_TARGET_S390X_UNKNOWN_LINUX_GNU_LINKER=s390x-linux-gnu-gcc