Build ext separately in nightly

[mvorisek]

Description

Currently, the build is tested in CI for building all ext together with the main php.

This is fine for testing the functionality, but basically any ext build can be broken due configure/linking issues.

This is a feature request to build all ext separately in one extra nightly job to prevent issues like #12565, #13745, #13764 to happen again.

[drupol]

Building extensions individually is how it is done in Nix by default.

I also did a project from my own initiative which build all the Git tags from the PHP project every day, including branch snapshots, I can detect failures in builds very quickly, actually, faster than the PHP project itself.

Example:

• RFC: Add the RoundingMode enum #14833 (comment)
• 88da914#r143708340

[mvorisek]

@iluuu1994 what do you think about one nighly job for this?

[iluuu1994]

I'm not opposed to it, if it's not a big maintenance burden.