sema: clean-up `{union,struct}FieldAlignment` and friends

My main gripes with this design were that it was incorrectly namespaced, the naming was inconsistent and a bit wrong (`fooAlign` vs `fooAlignment`).

This commit moves all the logic from `PerThread.zig` to use the zcu + tid system that the previous couple commits introduce.
I've organized and merged the functions to be a bit more specific to their own purpose.

- `fieldAlignment` takes a struct or union type, an index, and a Zcu (or the Sema version which takes a Pt), and gives you the alignment of the field at the index.
- `structFieldAlignment` takes the field type itself, and provides the logic to handle special cases, such as externs.

A design goal I had in mind was to avoid using the word 'struct' in the function name, when it worked for things that aren't structs, such as unions.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/codegen/c.zig b/src/codegen/c.zig
index d188435c3e..754286d80b 100644
--- a/src/codegen/c.zig
+++ b/src/codegen/c.zig
@@ -7206,7 +7206,7 @@ fn airAggregateInit(f: *Function, inst: Air.Inst.Index) !CValue {
                     var empty = true;
                     for (0..elements.len) |field_index| {
                         if (inst_ty.structFieldIsComptime(field_index, zcu)) continue;
-                        const field_ty = inst_ty.structFieldType(field_index, zcu);
+                        const field_ty = inst_ty.fieldType(field_index, zcu);
                         if (!field_ty.hasRuntimeBitsIgnoreComptime(zcu)) continue;
 
                         if (!empty) {
@@ -7219,7 +7219,7 @@ fn airAggregateInit(f: *Function, inst: Air.Inst.Index) !CValue {
                     empty = true;
                     for (resolved_elements, 0..) |element, field_index| {
                         if (inst_ty.structFieldIsComptime(field_index, zcu)) continue;
-                        const field_ty = inst_ty.structFieldType(field_index, zcu);
+                        const field_ty = inst_ty.fieldType(field_index, zcu);
                         if (!field_ty.hasRuntimeBitsIgnoreComptime(zcu)) continue;
 
                         if (!empty) try writer.writeAll(", ");