Fails to build on SL6.9 because of old unity version C99 incompatibility

[bl0x]

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Issue description

Build fails with error message because of C99 style variable initialisation in bundled unity framework.

Environment

• libzmq version (commit hash if unreleased):
  commit a8d1905
• OS:
  Scientific Linux 6.9
• Compiler:
  gcc 4.4.7

Minimal test code / Steps to reproduce the issue

1. Compilation fails

What's the actual result? (include assertion message & call stack if applicable)

[ 49%] Building C object tests/CMakeFiles/unity.dir/__/external/unity/unity.c.o
/home/AMS/drasiams/libzmq/external/unity/unity.c: In function ‘UnityParseOptions’:
/home/AMS/drasiams/libzmq/external/unity/unity.c:1408: error: ‘for’ loop initial declarations are only allowed in C99 mode
/home/AMS/drasiams/libzmq/external/unity/unity.c:1408: note: use option -std=c99 or -std=gnu99 to compile your code

What's the expected result?

Compilation should succeed.

[bluca]

This works fine in our CI (afaik CentOS 6 has the same base as SL6, same GCC version):

https://build.opensuse.org/build/network:messaging:zeromq:git-stable/CentOS_6/x86_64/libzmq/_log

Looks like a problem in your build environment or in CMake, can you use autotools instead?

[bluca]

ah I see the problem - in autoconf we set std=c99, but in cmake we don't. If you want to use cmake, can you send a PR to fix that?

[bluca]

basically this IF needs an ELSE that sets -std=gnu99: https://github.com/zeromq/libzmq/blob/master/CMakeLists.txt#L68

[bl0x]

Opened PR #3605 to fix this issue.

[bl0x]

I've tried using autotools, but the version of autoconf is too old. 2.63 instead of required 2.64.

When using autoconf from another machine to produce the configure.sh script, autotools build succeeds on SL6.9 without any change required.

[bluca]

@bl0x thanks for the PR, 2 suggestions:

1. We publish make-dist tarballs which means you don't have to use autotools, the configure is provided, eg: https://github.com/zeromq/libzmq/releases/download/v4.3.2/zeromq-4.3.2.tar.gz
2. On most Linux distros and architectures we also provide packages so you don't have to rebuild at all, and CentOS 6 is included: https://software.opensuse.org/download.html?project=network%3Amessaging%3Azeromq%3Arelease-stable&package=zeromq-devel

[bl0x]

Thank you for these suggestions.
In the current case I had no permission to install a package on the machine in question.