Build both Python 2 and Python 3 on x86 dist builders

Python 2 is needed for Clang 10, Python 3 for LLVM 12.

The Python 2 dependency could be removed by upgrading to Clang 11,
but that causes linker errors of unclear origin.

Author: nikic

src/ci/docker/host-x86_64/dist-i686-linux/Dockerfile

@@ -68,11 +68,13 @@ RUN ./build-binutils.sh
 COPY host-x86_64/dist-x86_64-linux/build-gcc.sh /tmp/
 RUN ./build-gcc.sh && apt-get remove -y gcc g++
 
-# Debian 6 has Python 2.6 by default, but LLVM needs 2.7+
 COPY host-x86_64/dist-x86_64-linux/build-python.sh /tmp/
-RUN ./build-python.sh
+# Build Python 2.7 needed for Clang 10.
+RUN ./build-python.sh 2.7.12
+# Build Python 3 needed for LLVM 12.
+RUN ./build-python.sh 3.9.1
 
-# LLVM needs cmake 3.4.3 or higher, and is planning to raise to 3.13.4.
+# LLVM needs cmake 3.13.4 or higher.
 COPY host-x86_64/dist-x86_64-linux/build-cmake.sh /tmp/
 RUN ./build-cmake.sh
 

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

@@ -68,11 +68,13 @@ RUN ./build-binutils.sh
 COPY host-x86_64/dist-x86_64-linux/build-gcc.sh /tmp/
 RUN ./build-gcc.sh && apt-get remove -y gcc g++
 
-# Debian 6 has Python 2.6 by default, but LLVM needs 2.7+
 COPY host-x86_64/dist-x86_64-linux/build-python.sh /tmp/
-RUN ./build-python.sh
+# Build Python 2.7 needed for Clang 10.
+RUN ./build-python.sh 2.7.12
+# Build Python 3 needed for LLVM 12.
+RUN ./build-python.sh 3.9.1
 
-# LLVM needs cmake 3.4.3 or higher, and is planning to raise to 3.13.4.
+# LLVM needs cmake 3.13.4 or higher.
 COPY host-x86_64/dist-x86_64-linux/build-cmake.sh /tmp/
 RUN ./build-cmake.sh
 

src/ci/docker/host-x86_64/dist-x86_64-linux/build-python.sh

@@ -3,7 +3,8 @@
 set -ex
 source shared.sh
 
-curl https://www.python.org/ftp/python/2.7.12/Python-2.7.12.tgz | \
+VERSION=$1
+curl https://www.python.org/ftp/python/$VERSION/Python-$VERSION.tgz | \
   tar xzf -
 
 mkdir python-build
@@ -12,10 +13,10 @@ cd python-build
 # Gotta do some hackery to tell python about our custom OpenSSL build, but other
 # than that fairly normal.
 CFLAGS='-I /rustroot/include' LDFLAGS='-L /rustroot/lib -L /rustroot/lib64' \
-    hide_output ../Python-2.7.12/configure --prefix=/rustroot
+    hide_output ../Python-$VERSION/configure --prefix=/rustroot
 hide_output make -j10
 hide_output make install
 
 cd ..
 rm -rf python-build
-rm -rf Python-2.7.12
+rm -rf Python-$VERSION