migrate to the restructured sx stdlib paths

modules/compiler.sx -> modules/build.sx; stb/stb_truetype/opengl/sdl3 ->
modules/ffi/; modules/process.sx -> modules/std/process.sx. Rebuilt for
macos + ios-sim; 23/23 logic snapshots pass.

tests/test.sx

@@ -5,7 +5,7 @@
 // terminates the process NON-ZERO (exit 1) via process.exit, so a broken
 // assertion fails `tools/run_tests.sh` and the build gate.
 #import "modules/std.sx";
-proc :: #import "modules/process.sx";
+proc :: #import "modules/std/process.sx";
 
 expect :: (cond: bool, msg: string, loc: Source_Location = #caller_location) {
     if !cond {