allow cross-compiling liblcf with autotools for big endian systems like wii

This allows to do
```
./configure --host=powerpc-eabi --prefix="$DEVKITPRO/portlibs/ppc" CXXFLAGS="-O2 -mcpu=750 -meabi -mhard-float"
make
make install
```
and use liblcf as all other portlibs for wii development.

Before this is ready, however, liblcf headers should be installed in subfolder (cleaner).
The old method of compiling (extracting/cloning in lib folder) is still supported, a safeguard against redefining ```LCF_BIG_ENDIAN``` is included.

A downside of the ```AC_C_BIGENDIAN``` macro is, that it is not guranteed to function when cross-compiling and when building universal binaries for mac os (ppc/intel).