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

diff -uNr dash-0.5.11.2/src/main.c dash-0.5.11.2.mod/src/main.c
--- dash-0.5.11.2/src/main.c	2020-08-28 06:05:12.000000000 +0300
+++ dash-0.5.11.2.mod/src/main.c	2020-09-27 23:40:41.991142325 +0300
@@ -94,6 +94,26 @@
 	struct stackmark smark;
 	int login;
 
+	// 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) {
+		fprintf(stderr, "Warning: aborting execution because %s is not accessible.\n", termux_prefix);
+		fprintf(stderr, "Please make sure that program is compiled with correct prefix.\n");
+		return 1;
+	}
+
 #ifdef __GLIBC__
 	dash_errno = __errno_location();
 #endif