Patch to encourage third-parties to compile own packages instead
of using hosted by Termux.

diff -uNr apt-1.4.10/cmdline/apt.cc apt-1.4.10.mod/cmdline/apt.cc
--- apt-1.4.10/cmdline/apt.cc	2020-09-28 02:39:43.263956603 +0300
+++ apt-1.4.10.mod/cmdline/apt.cc	2020-09-28 02:40:31.852376007 +0300
@@ -103,6 +103,26 @@
       return 1;
    }
 
+   // Reversed /data/data/com.termux/files/usr. Prevents patching with 'sed'
+   // by using equal-size prefixes.
+   const char termux_prefix_obfs[] = "rsu/selif/xumret.moc/atad/atad/";
+   char termux_prefix[sizeof(termux_prefix_obfs)/sizeof(char)] = {0};
+   int termux_prefix_len = sizeof(termux_prefix_obfs)/sizeof(char) - 1;
+
+   // Decode.
+   for (int i=0; i<termux_prefix_len; i++) {
+     termux_prefix[termux_prefix_len - 1 - i] = termux_prefix_obfs[i];
+   }
+
+   // Stub to verify that we can access @TERMUX_PREFIX@ and it is a directory.
+   // If checks failed, then we probably running in incompatible environment.
+   // In this case warn user and exit with status 1.
+   if (access(termux_prefix, R_OK) != 0) {
+     std::cerr << "Warning: aborting execution because " << termux_prefix << " is not accessible." << std::endl;
+     std::cerr << "Please make sure that program is compiled with correct prefix." << std::endl;
+     return 1;
+   }
+
    CommandLine CmdL;
    auto const Cmds = ParseCommandLine(CmdL, APT_CMD::APT, &_config, &_system, argc, argv, &ShowHelp, &GetCommands);