All the other files in the repo which include bitcoin-config.h do so with the appropriate subfolder prefixed: config/bitcoin-config.h
The header should be included with the appropriate subfolder here as well.
This canonicalization also allows getting rid of a bit of extra configuration in Makefile.am.
- Detect endian instead of stopping configure on big-endian
- Add `byteswap.h` and `endian.h` header for compatibility with
Windows and other operating systems that don't come with them
- Update `crypto/common.h` functions to use compat
endian header