Compile MRPT on ARM board

1. add #define _POSIX_PATH_MAX 255 where mrpt-0.9.5/otherlibs/gtest-1.5.0/fused-src/gtest
2. Replace fabsl() to fabs()
3. Replace __atomic_add to __gnu_cxx::__atomic_add where libs/base/src/synch/atomic_incr.cpp
~/src$ cd build
~/src/build$ cmake -DCMAKE_TOOLCHAIN_FILE=~/Toolchain-arm-x86.cmake ..