Cleanup endian checks

[schwehr]

There should be only on place that checks for endian and it should be at compile time.

What do autoconf and CMake say about endianness?

• AC_C_BIGENDIAN
• TEST_BIG_ENDIAN

https://stackoverflow.com/questions/2100331/c-macro-definition-to-determine-big-endian-or-little-endian-machine

http://esr.ibiblio.org/?p=5095

[thbeu]

What is your preferred way to fix this? Is a global variable bigEndian required?

I used this kind of "static" endian detection in matio which is working for years:

https://github.com/tbeu/matio/blob/0884b80a7ee5783b6193d7e2c58f997d121d3245/src/mat4.c#L153-L173

[thbeu]

@schwehr I see that you self-assigned this issue, but nevertheless I now created #91.

[schwehr]

Awesome! I ran out of steam working on shapelib and I appreciate you doing #91.