Correctly print interfaces.

lib/std/core/allocators/libc_allocator.c3

@@ -3,15 +3,20 @@
 // a copy of which can be found in the LICENSE_STDLIB file.
 
 module std::core::mem::allocator @if(env::LIBC);
+import std::io;
 import libc;
 
 const LibcAllocator LIBC_ALLOCATOR = {};
-distinct LibcAllocator (Allocator) = uptr;
+distinct LibcAllocator (Allocator, Printable) = uptr;
+
+fn String LibcAllocator.to_string(&self, Allocator allocator) @dynamic => "Libc allocator".copy(allocator);
+fn usz! LibcAllocator.to_format(&self, Formatter *format) @dynamic => format.print("Libc allocator");
 
 module std::core::mem::allocator @if(env::POSIX);
 import std::os;
 import libc;
 
+
 fn void*! LibcAllocator.acquire(&self, usz bytes, AllocInitType init_type, usz alignment) @dynamic
 {
 	if (init_type == ZERO)

lib/std/io/formatter.c3

@@ -117,6 +117,7 @@ fn usz! Formatter.out_str(&self, any arg) @private
 		case ANYFAULT:
 		case FAULT:
 			return self.out_substr((*(anyfault*)arg.ptr).nameof);
+		case INTERFACE:
 		case ANY:
 			return self.out_str(*(any*)arg);
 		case OPTIONAL:
@@ -282,6 +283,9 @@ fn usz! Formatter.out_str(&self, any arg) @private
 			}
 			len += self.out(']')!;
 			return len;
+		case ANY:
+		case INTERFACE:
+			unreachable("Already handled");
 		default:
 	}
 	return self.out_substr("Invalid type");