And make locatable by via `php-config`. Prior to this, `libphp.*`
would always install to `$prefix/lib`. After this, they will install
to `$libdir`.
In practice, this will make it so that programs embedding libphp can
use `php-config` to determine appropriate compile flags without
guessing.
In `configure.ac`, it seems `$libdir` is mutated in some instances.
Ideally the mutated version would be stored in `$phplibdir` or
something. Instead of tracking down all uses of that variable, I
introduced another variable `$orig_libdir` that holds the original
value passed to the configure script.
This is a no-op for users unless they are compiling with `--libdir`
set to something other than `$prefix/lib`, the default.
Closes GH-12389
0c07b0d94f