Android: fix horrible libiconv build

Before, our libiconv build was a joke. We first called configure for our own build host system,
then called make, before we executed a Android.mk script we provided as patch. The first "native make"
always failed, and the LIBICONV_LIB file setting in our Makefile didn't match the built one,
resulting in an always-rebuild of iconv.

This commit cleans up this total mess, removes the double-build, and the Android.mk, and properly calls
./configure with the according target platform, and uses a built toolchain.

As we have to deal with the android bug "NDK: Support for prebuild libs with full sonames"
https://code.google.com/p/android/issues/detail?id=55868
as the 2013 patch
https://lists.gnu.org/archive/html/libtool-patches/2013-06/msg00002.html
by Google's David Turner wasn't inside the 2011 libtool, we pass -avoid-version to
libtool.

Thanks to the proper build, wide_to_utf8 works for android now, removing us of the need to disable it.

src/util/string.cpp

@@ -102,16 +102,6 @@ std::wstring utf8_to_wide(const std::string &input)
 	return out;
 }
 
-#ifdef __ANDROID__
-
-// TODO: this is an ugly fix for wide_to_utf8 somehow not working on android
-std::string wide_to_utf8(const std::wstring &input)
-{
-	return wide_to_narrow(input);
-}
-
-#else // __ANDROID__
-
 std::string wide_to_utf8(const std::wstring &input)
 {
 	size_t inbuf_size = (input.length() + 1) * sizeof(wchar_t);
@@ -138,8 +128,6 @@ std::string wide_to_utf8(const std::wstring &input)
 	return out;
 }
 
-#endif // __ANDROID__
-
 #else // _WIN32
 
 std::wstring utf8_to_wide(const std::string &input)