Simplify sqlite3mc build

[penberg]

We currently build sqlite3mc by invoking its cmake-based build, which makes the build more complicated, especially when cross-compiling. Let's look into switching to using the cc crate from libsql-ffi/build.rs instead to simplify the build.

[levydsa]

I'm looking into this. I think the best approach is to ditch the whole amalgamation thing and merge both sqlite3 and sqlite3mc in the same repo, then toggle the later with a flag as needed (I think there already is one, not sure). I'm currently exploring the use of Zig's build system, but adding this as a dependency might be undesirable.

#1039 is somewhat related