Fix #298: lib expects existence of stpcpy, so fake it in executable.

(Because the library is built at API >= 21 and the executable isn't.)

app/build.gradle

@@ -124,6 +124,7 @@ android.applicationVariants.all{ variant ->
             abiParam,
             'NDK_LOG=1',
             'NDK_DEBUG=' + (variant.ndkCompile.debuggable ? '1' : '0')]
+        // You must remove the fake stpcpy implementation in android-gen.c when increasing APP_PLATFORM to >= 21
         exec {
             commandLine common + [
                     'APP_PLATFORM=android-9',  // 9 is earliest for x86 + mips

app/src/main/jni/android-gen.c

@@ -1,9 +1,18 @@
 #ifdef EXECUTABLE
 #include <stdio.h>
+#include <string.h>
 #include "puzzles.h"
 
 #define USAGE "Usage: puzzles-gen gamename [params | --seed seed | --desc desc]\n"
 
+/* https://github.com/chrisboyle/sgtpuzzles/issues/298 */
+char *
+stpcpy(char *dst, char const *src)
+{
+	size_t src_len = strlen(src);
+	return memcpy(dst, src, src_len) + src_len;
+}
+
 struct frontend {
 	midend *me;
 };