Optimize layer sizes

[mnapoli]

The goal is to reduce layer sizes to optimize cold starts (that's the theory at least).

• strip debug symbols for all libraries and PHP extensions (saves 11.7%)
• compile PHP with the -Os C/CPP flag to optimize the binary for size (saves 8%)
• compile libraries with the -Os flag (saves 6.3%)
• disable the soap extension by default to avoid loading it on PHP startup (the only big unpopular extension I could find)
• bundle the pdo-mysql extension in the PHP binary: it is extra small and will avoid loading it through an external file (small optimization)

In total that's a 24% size reduction, i.e. 14.6MB.

This is for Bref v3, I will run some benchmarks as just measuring the layer size doesn't tell us the full story about cold starts.

[GrahamCampbell]

compile PHP with the -Os C/CPP flag to optimize the binary for size (saves 8%)

This could probably be backported to bref 2 without any issues.

[mnapoli]

Yes but there is some uncertainty on whether -Os is worth it over -O3 or even -O2 in terms of performance, so I'd feel much more comfortable being able to have a long beta period where multiple people can beta test these changes.

[GrahamCampbell]

Ah, good point. -O1 or even -O2 are probably quite conservative options to go with in Bref 2, if we wanted.

[GrahamCampbell]

Asking Claude what it thinks...

[mnapoli]

I'll run some benchmarks and see if there is any noticeable change