Make sure _simple_handler is not exported
Make sure _simple_handler is not exported

Support for simple signal handling was added in
a0a417240e69a9951e92b57c8d7fb328e437c71d. This commit also adds the
`_simple_handler` function. It seems to me that this function is
intended as a helper function which should only be visible in
`idris_signal.c`, it is not used outside this file. For this purpose it
is probably also marked as inline. However, the inline keyword does not
require the compiler to actually inline the function. As such, the
`_simple_handler` symbol may still be exported if the compiler doesn't
inline the function.

On my system this seems to be the case and causes the following error
during compilation of idris2:

	Exception: (while loading libidris2_support.so) Error relocating Idris2-0.4.0/build/exec/idris2_app/libidris2_support.so: _simple_handler: symbol not found

By marking the `_simple_handler` function as `static inline` it is
ensured that the symbol is not exported, thereby preventing the
relocation error.

mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm,mmhelloworld/idris-jvm