Make build hermetic without shell scripts

- Fix some minor issues in ar.com
- Have execve() look for `ape` command
- Rewrite NT paths using /c/ rather /??/c:/
- Replace broken GCC symlinks with .sym files
- Rewrite $PATH environment variables on startup
- Make $(APE_NO_MODIFY_SELF) the default bootloader
- Add all build command dependencies to build/bootstrap
- Get the repository mostly building from source on non-Linux

tool/build/unbundle.c

@@ -0,0 +1,89 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2022 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/calls.h"
+#include "libc/calls/struct/stat.h"
+#include "libc/dce.h"
+#include "libc/errno.h"
+#include "libc/fmt/itoa.h"
+#include "libc/runtime/runtime.h"
+#include "libc/stdio/stdio.h"
+#include "libc/str/str.h"
+#include "libc/x/x.h"
+#include "third_party/musl/ftw.h"
+
+const char *prog;
+char tmpdir[PATH_MAX];
+char binpath[PATH_MAX];
+
+bool IsDirectory(const char *path) {
+  int e;
+  bool res;
+  struct stat st;
+  e = errno;
+  res = stat(path, &st) != -1 && S_ISDIR(st.st_mode);
+  errno = e;
+  return res;
+}
+
+void Execute(char *argv[]) {
+  int ws;
+  if (!vfork()) {
+    execv(argv[0], argv);
+    _Exit(127);
+  }
+  wait(&ws);
+  if (!WIFEXITED(ws) || WEXITSTATUS(ws)) {
+    fputs(argv[0], stderr);
+    fputs(": command failed\n", stderr);
+    exit(1);
+  }
+}
+
+int Visit(const char *fpath, const struct stat *sb, int tflag,
+          struct FTW *ftwbuf) {
+  if (tflag == FTW_F && endswith(fpath, ".gz")) {
+    Execute((char *[]){"build/bootstrap/gzip.com", "-d", fpath, 0});
+    strcpy(binpath, fpath);
+    binpath[strlen(binpath) - 3] = 0;
+    chmod(binpath, 0755);
+  } else if (tflag == FTW_F && endswith(fpath, ".sym")) {
+    strcpy(binpath, fpath);
+    binpath[strlen(binpath) - 4] = 0;
+    symlink(xslurp(fpath, 0), binpath);
+  }
+  return 0;
+}
+
+int main(int argc, char *argv[]) {
+  if (!IsLinux()) return 0;
+  prog = argc > 0 ? argv[0] : "unbundle.com";
+  if (IsDirectory("o/third_party/gcc")) return 0;
+  makedirs("o/third_party", 0755);
+  FormatInt32(stpcpy(tmpdir, "o/third_party/gcc."), getpid());
+  Execute(
+      (char *[]){"build/bootstrap/cp.com", "-r", "third_party/gcc", tmpdir, 0});
+  if (nftw(tmpdir, Visit, 20, 0) == -1) {
+    fputs(prog, stderr);
+    fputs(": nftw failed: ", stderr);
+    fputs(strerdoc(errno), stderr);
+    fputs("\n", stderr);
+    exit(1);
+  }
+  rename(tmpdir, "o/third_party/gcc");
+}