Update dist-s390x-dist image

Update to Ubuntu 20.04 and crosstool-ng 1.24.0. I've updated the
ct-ng config and then manually reset the kernel and glibc versions
to the oldest supported.

Specifically, we're updating from kernel 2.6.32.68 to 2.6.32.71
and glibc 2.11.1 to 2.12.1 here. The compiler toolchain is also
updated, but I don't think that's relevant for compatibility.

Author: nikic

src/ci/docker/README.md

@@ -271,8 +271,8 @@ For targets: `s390x-unknown-linux-gnu`
 - Target options > Target Architecture = s390
 - Target options > Bitness = 64-bit
 - Operating System > Target OS = linux
-- Operating System > Linux kernel version = 2.6.32.68 -- ~RHEL6 kernel
-- C-library > glibc version = 2.11.1 -- ~SLE11-SP4 glibc
-- C compiler > gcc version = 5.2.0
+- Operating System > Linux kernel version = 2.6.32.71 -- ~RHEL6 kernel
+- C-library > glibc version = 2.12.1 -- ~RHEL6 glibc
+- C compiler > gcc version = 8.3.0
 - C compiler > gcc extra config = --with-arch=z10 -- LLVM's minimum support
 - C compiler > C++ = ENABLE -- to cross compile LLVM

src/ci/docker/host-x86_64/dist-s390x-linux/Dockerfile

@@ -1,15 +1,10 @@
-FROM ubuntu:16.04
+FROM ubuntu:20.04
 
 COPY scripts/cross-apt-packages.sh /scripts/
 RUN sh /scripts/cross-apt-packages.sh
 
-# Ubuntu 16.04 (this container) ships with make 4, but something in the
-# toolchains we build below chokes on that, so go back to make 3
-COPY scripts/make3.sh /scripts/
-RUN sh /scripts/make3.sh
-
-COPY scripts/crosstool-ng.sh /scripts/
-RUN sh /scripts/crosstool-ng.sh
+COPY scripts/crosstool-ng-1.24.sh /scripts/
+RUN sh /scripts/crosstool-ng-1.24.sh
 
 COPY scripts/rustbuild-setup.sh /scripts/
 RUN sh /scripts/rustbuild-setup.sh
@@ -37,5 +32,5 @@ ENV \
 
 ENV HOSTS=s390x-unknown-linux-gnu
 
-ENV RUST_CONFIGURE_ARGS --enable-extended --disable-docs
+ENV RUST_CONFIGURE_ARGS --enable-extended --enable-lld --disable-docs
 ENV SCRIPT python3 ../x.py dist --host $HOSTS --target $HOSTS