Found and fixed problem with recent GTest revisions

* __FLOAT_H is defined both by our vm/vm/main/float.hh
  and Clang's float.h (usually /usr/lib/clang/5.0/include/float.h).
* It might also be considered as a problem of Clang
  (other #define have weird names or start with __CLANG_).
Merge pull request #146 from eregon/bad_define

Found and fixed problem with recent GTest revisions