precompile and cache Carbon prelude (#7432)

Refactors the link driver to automatically compile and cache the carbon
prelude for use in linking.

Implements a `carbon_library` rule for compiling the Core library
dependencies in the examples.

core/BUILD

@@ -2,13 +2,13 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+load("//bazel/carbon_rules:defs.bzl", "carbon_library")
 load("//bazel/manifest:defs.bzl", "manifest")
 
 # Raw prelude files.
-# TODO: This includes all of Core, not just the prelude.
 filegroup(
     name = "prelude_files",
-    srcs = glob(["**/*.carbon"]),
+    srcs = ["prelude.carbon"] + glob(["prelude/**/*.carbon"]),
     visibility = ["//visibility:public"],
 )
 
@@ -29,3 +29,43 @@ filegroup(
     ],
     visibility = ["//visibility:public"],
 )
+
+filegroup(
+    name = "core_library_files",
+    srcs = glob(
+        include = ["**/*.carbon"],
+        exclude = [
+            "prelude.carbon",
+            "prelude/**",
+        ],
+    ),
+    visibility = ["//visibility:public"],
+)
+
+manifest(
+    name = "core_library_manifest.txt",
+    srcs = [":core_library_files"],
+    strip_package_dir = True,
+)
+
+filegroup(
+    name = "core_library",
+    srcs = [
+        ":core_library_files",
+        ":core_library_manifest.txt",
+    ],
+    visibility = ["//visibility:public"],
+)
+
+carbon_library(
+    name = "io",
+    api = "io.carbon",
+    impls = ["io.impl.carbon"],
+    visibility = ["//visibility:public"],
+)
+
+carbon_library(
+    name = "range",
+    api = "range.carbon",
+    visibility = ["//visibility:public"],
+)

core/io.carbon

@@ -7,24 +7,15 @@
 
 package Core library "io";
 
-import library "prelude";
-
 // TODO: Support printing other types.
 // TODO: Consider rewriting using native support once library support exists.
 fn Print(x: i32) = "print.int";
 fn PrintChar(x: char) -> i32 = "print.char";
 
-fn PrintStr(msg: str) {
-  let size: i64 = msg.Size() as i64;
-  var i: i64 = 0;
-  while (i < size) {
-    PrintChar(msg[i]);
-    ++i;
-  }
-}
+fn PrintStr(msg: str);
 
 // TODO: Return an `Optional(char)` instead of `i32`.
 fn ReadChar() -> i32 = "read.char";
 
 // TODO: Change this to a global constant once they are fully supported.
-fn EOF() -> i32 { return -1; }
+fn EOF() -> i32;

core/io.impl.carbon

@@ -0,0 +1,20 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// TODO: This library is not part of the design. Either write a matching
+// proposal or remove this.
+
+impl package Core library "io";
+
+fn PrintStr(msg: str) {
+  let size: i64 = msg.Size() as i64;
+  var i: i64 = 0;
+  while (i < size) {
+    PrintChar(msg[i]);
+    ++i;
+  }
+}
+
+// TODO: Change this to a global constant once they are fully supported.
+fn EOF() -> i32 { return -1; }

core/range.carbon

@@ -7,15 +7,6 @@
 
 package Core library "range";
 
-import library "prelude/destroy";
-import library "prelude/iterate";
-import library "prelude/operators/arithmetic";
-import library "prelude/operators/as";
-import library "prelude/operators/comparison";
-import library "prelude/types/int";
-import library "prelude/types/int_literal";
-import library "prelude/types/optional";
-
 class IntRange(N: IntLiteral) {
   fn Make(start: Int(N), end: Int(N)) -> Self {
     return {.start = start, .end = end};