Fix compilation of JSON library with Android NDK

[honggoff]

The JSON library used in this project contains a workaround for an old version of the Android NDK. On a current NDK, this leads to a duplicate declaration of wcsncasecmp.

Compile the native libraries with -UANDROID to disable the troublesome workaround.

I'm using the ndk-bundle that is installed by the Android SDK manager. I run the build using the gradle wrapper and it uses the following compiler: dk-bundle/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++

The compile error this fixes looks as follows:

In file included from /home/hong/git/passman-android/app/src/main/cpplibs/SimpleJSON/src/JSON.cpp:25:
../../../../src/main/cpplibs/SimpleJSON/src/JSON.h:50:20: error: static declaration of 'wcsncasecmp' follows non-static declaration
      static inline int wcsncasecmp(const wchar_t *s1, const wchar_t *s2, size_t n)
                        ^
.../Android/Sdk/ndk-bundle/sysroot/usr/include/wchar.h:121:19: note: previous declaration is here
int               wcsncasecmp(const wchar_t *, const wchar_t *, size_t);
                  ^

[animalillo]

You didn't gpg sign you commit.