This avoids the need to use "yum update && yum upgrade" in the container
to be able to contact GitHub, which requires TLS 1.2[1].
I have verified that binaries built with this container still run in the
previous container; no errors like "/lib64/libc.so.6: version
`GLIBC_2.14' not found", which occur if using too new of a glibc when
compiling. CentOS 6.6 has glibc version 2.12 release 1.209.el6. CentOS
6.9 has glibc version 2.12 release 1.149.el6. Both would upgrade to
release 1.212.el6 via "yum update && yum upgrade".
1. https://githubengineering.com/crypto-deprecation-notice/
Now that we depend on C++11, we need at least GCC 4.8 instead of 4.7.
This change updates the Docker setup to continue using CentOS 6.6 but
with GCC 4.8.
I also added libm to the whitelist for dynamically linked libraries for
the ARM64 protoc binary.
ENTRYPOINT is used even when other commands are specified on the "docker
run" command line. This allows running one-off commands in the docker
image (especially combined with volume binding with the host) with the
correct environment variables.
It is a bad idea to check out code into the docker image, as it will be
out-of-date. It is better to have the image just be the environment, and
let any scripts that need source check them out themselves.
This fixes#4419 in that it allows the image to build again, albeit
users would need to use wget to grab the source of the version of
protobuf they wish.
