compile error for C pointer with align attribute

See #1059

Author: andrewrk

src/ir.cpp

@@ -5057,6 +5057,11 @@ static IrInstruction *ir_gen_pointer_type(IrBuilder *irb, Scope *scope, AstNode
 
     IrInstruction *align_value;
     if (align_expr != nullptr) {
+        if (ptr_len == PtrLenC) {
+            exec_add_error_node(irb->codegen, irb->exec, node,
+                buf_sprintf("[*c] pointers may not have align attribute"));
+            return irb->codegen->invalid_instruction;
+        }
         align_value = ir_gen_node(irb, align_expr, scope);
         if (align_value == irb->codegen->invalid_instruction)
             return align_value;

test/compile_errors.zig

@@ -118,13 +118,17 @@ pub fn addCases(cases: *tests.CompileErrorContext) void {
     );
 
     cases.addTest(
-        "C pointer pointing to non C ABI compatible type",
+        "C pointer pointing to non C ABI compatible type or has align attr",
         \\const Foo = struct {};
-        \\export fn entry() [*c]Foo {
-        \\    return undefined;
+        \\export fn a() void {
+        \\    const T = [*c]Foo;
+        \\}
+        \\export fn b() void {
+        \\    const T = [*c]align(4) u8;
         \\}
     ,
-        ".tmp_source.zig:2:19: error: C pointers cannot point to non-C-ABI-compatible type 'Foo'",
+        ".tmp_source.zig:3:15: error: C pointers cannot point to non-C-ABI-compatible type 'Foo'",
+        ".tmp_source.zig:6:15: error: [*c] pointers may not have align attribute",
     );
 
     cases.addTest(

test/stage1/behavior/type_info.zig

@@ -67,12 +67,12 @@ test "type info: C pointer type info" {
 }
 
 fn testCPtr() void {
-    const ptr_info = @typeInfo([*c]align(4) const i8);
+    const ptr_info = @typeInfo([*c]const i8);
     expect(TypeId(ptr_info) == TypeId.Pointer);
     expect(ptr_info.Pointer.size == TypeInfo.Pointer.Size.C);
     expect(ptr_info.Pointer.is_const);
     expect(!ptr_info.Pointer.is_volatile);
-    expect(ptr_info.Pointer.alignment == 4);
+    expect(ptr_info.Pointer.alignment == 1);
     expect(ptr_info.Pointer.child == i8);
 }