jni: fix C99 inline linking

Clang builds C code according to the C99 standard,
which provides different semantics for the inline
keyword than GCC's default behavior. This is the
correct behavior without any gnu extensions.

See here:
http://clang.llvm.org/compatibility.html#inline

Change-Id: I831a5189e027a2f0cb3c7d9cda56bd3701502863
Optipng -nc -nb -o7

Change-Id: I1df1f2fbb25d0835ba942e8dfdf4415bb2b83c0d