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/readlinkat-nt.c

@@ -58,10 +58,9 @@ textwindows ssize_t sys_readlinkat_nt(int dirfd, const char *path, char *buf,
         p = (char16_t *)((char *)rdb->SymbolicLinkReparseBuffer.PathBuffer +
                          rdb->SymbolicLinkReparseBuffer.PrintNameOffset);
         if (n >= 3 && isalpha(p[0]) && p[1] == ':' && p[2] == '\\') {
-          buf[j++] = '/';
-          buf[j++] = '/';
-          buf[j++] = '?';
-          buf[j++] = '/';
+          p[1] = p[0];
+          p[0] = '/';
+          p[2] = '/';
         }
         while (i < n) {
           x = p[i++] & 0xffff;