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

libc/calls/execve-sysv.c

@@ -16,28 +16,80 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/bits/bits.h"
 #include "libc/bits/safemacros.internal.h"
 #include "libc/calls/calls.h"
 #include "libc/calls/syscall-sysv.internal.h"
 #include "libc/errno.h"
 #include "libc/mem/alloca.h"
 #include "libc/paths.h"
+#include "libc/runtime/runtime.h"
 #include "libc/str/str.h"
+#include "libc/sysv/consts/at.h"
+#include "libc/sysv/consts/o.h"
+#include "libc/sysv/consts/ok.h"
+#include "libc/sysv/errfuns.h"
+
+static bool CanExecute(const char *path) {
+  return !sys_faccessat(AT_FDCWD, path, X_OK, 0);
+}
+
+static bool IsApeBinary(const char *path) {
+  int fd;
+  char buf[8];
+  bool res = false;
+  if ((fd = sys_open(path, O_RDONLY, 0)) != -1) {
+    if (sys_read(fd, buf, 8) == 8 && READ64LE(buf) == READ64LE("MZqFpD='")) {
+      res = true;
+    }
+    sys_close(fd);
+  }
+  return res;
+}
+
+static const char *Join(const char *a, const char *b, char buf[PATH_MAX]) {
+  size_t n, m;
+  n = strlen(a);
+  m = strlen(b);
+  if (n + 1 + m + 1 < PATH_MAX) {
+    stpcpy(stpcpy(stpcpy(buf, a), "/"), b);
+    return buf;
+  } else {
+    return "";
+  }
+}
 
 int sys_execve(const char *prog, char *const argv[], char *const envp[]) {
+  int e;
   size_t i;
+  char *buf;
   char **shargs;
+  const char *ape;
+  e = errno;
   __sys_execve(prog, argv, envp);
   if (errno != ENOEXEC) return -1;
   for (i = 0; argv[i];) ++i;
-  shargs = alloca((i + 2) * sizeof(char *));
-  memcpy(shargs + 2, argv + 1, i * sizeof(char *));
-  if (IsFreebsd() || IsNetbsd()) {
-    shargs[0] = firstnonnull(commandv("bash", alloca(PATH_MAX), PATH_MAX),
-                             _PATH_BSHELL);
+  buf = alloca(PATH_MAX);
+  shargs = alloca((i + 4) * sizeof(char *));
+  if (IsApeBinary(prog) &&
+      (CanExecute((ape = "/usr/bin/ape")) ||
+       CanExecute(
+           (ape = Join(firstnonnull(getenv("TMPDIR"), "/tmp"), "ape", buf))))) {
+    shargs[0] = ape;
+    shargs[1] = "-";
+    shargs[2] = prog;
+    memcpy(shargs + 3, argv, (i + 1) * sizeof(char *));
+  } else if (CanExecute(prog)) {
+    if (IsFreebsd() || IsNetbsd()) {
+      shargs[0] = firstnonnull(commandv("bash", buf, PATH_MAX), _PATH_BSHELL);
+    } else {
+      shargs[0] = _PATH_BSHELL;
+    }
+    shargs[1] = prog;
+    memcpy(shargs + 2, argv + 1, i * sizeof(char *));
   } else {
-    shargs[0] = _PATH_BSHELL;
+    return enoexec();
   }
-  shargs[1] = prog;
+  errno = e;
   return __sys_execve(shargs[0], shargs, envp);
 }