Display Linux variant at ./configure time

[kinkie]

Linux standards offer an /etc/os-release file containing
information about the operating system.

Parse that file and print an identifier of the Linux version at
configure time.

[kinkie]

Sample output:

CenOS Stream 9

checking simplified host os... linux (version )
configure: Building on CentOS Stream 9
checking for gcc... ccache gcc

Debian Trixie

checking build system type... x86_64-pc-linux-gnux32
checking host system type... x86_64-pc-linux-gnux32
checking simplified host os... linux (version 32)
configure: Building on Debian GNU/Linux trixie/sid
checking for gcc... ccache gcc

Ubuntu Noble

checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking simplified host os... linux (version )
configure: Building on Ubuntu 24.04.1 LTS
checking for gcc... ccache gcc

Gentoo

checking host system type... i686-pc-linux-gnu
checking simplified host os... linux (version )
configure: Building on Gentoo Linux
checking for gcc... ccache gcc

MacOS

checking host system type... aarch64-apple-darwin24.1.0
checking simplified host os... darwin (version 24.1.0)
checking for gcc... gcc

[rousskov]

Thank you for this addition! I am sure this code can be enhanced to cover other OSes, but we do not have to do that in this PR.

While those grep commands can be merged into one and sed commands can be removed using unportable grep features like grep -P (available on Linux), keeping that part of code more portable might help in future enhancements.

I adjusted PR title to reduce "configuration" ambiguity and committed minor polishing touches. Please adjust further as needed -- I only insist on _cv_ removal.

[kinkie]

Thank you for this addition! I am sure this code can be enhanced to cover other OSes, but we do not have to do that in this PR.

While those grep commands can be merged into one and sed commands can be removed using unportable grep features like grep -P (available on Linux), keeping that part of code more portable might help in future enhancements.

I thought about it, but that wouldn't work:

$ grep NAME /etc/os-release
PRETTY_NAME="Ubuntu 24.04 LTS"
NAME="Ubuntu"
VERSION_CODENAME=noble
UBUNTU_CODENAME=noble

There really is no standardisation on the contents of /etc/os-release, it seems.
In other words, matching on "NAME=" would yield two lines on ubuntu, and we may make no assumptions about their order. Other distros do not provide a PRETTY_NAME at all.

We really need a logic like "try PRETTY_NAME, and if not available fall back on NAME"

I adjusted PR title to reduce "configuration" ambiguity and committed minor polishing touches. Please adjust further as needed -- I only insist on _cv_ removal.

I don't think coverin gother OSes will be necessary, they should be already covered by the "simplified host os" line above.

[rousskov]

I don't think coverin gother OSes will be necessary, they should be already covered by the "simplified host os" line above.

This is not my area of expertise. I am happy to assume that you are right. Do you want to try to remove those sed calls using non-portable Linux tricks? If not, then there is nothing else to do here.

[kinkie]

I don't think coverin gother OSes will be necessary, they should be already covered by the "simplified host os" line above.

This is not my area of expertise. I am happy to assume that you are right. Do you want to try to remove those sed calls using non-portable Linux tricks? If not, then there is nothing else to do here.

Nah, I'd leave as-is. We still want to adhere to best autoconf practices and make least assumptions possible on the host system.

[yadij]

Backported for 6.12