This fixes some gcc warnings such as:
```
Eigen/src/Core/GenericPacketMath.h:655:63: warning: implicit conversion turns floating-point number into bool: 'typename __gnu_cxx::__enable_if<__is_integer<bool>::__value, double>::__type' (aka 'double') to 'bool' [-Wimplicit-conversion-floating-point-to-bool]
Packet psqrt(const Packet& a) { EIGEN_USING_STD(sqrt); return sqrt(a); }
```
Details:
- Added `scalar_sqrt_op<bool>` (`-Wimplicit-conversion-floating-point-to-bool`).
- Added `scalar_square_op<bool>` and `scalar_cube_op<bool>`
specializations (`-Wint-in-bool-context`)
- Deprecated above specialized ops for bool.
- Modified `cxx11_tensor_block_eval` to specialize generator for
booleans (`-Wint-in-bool-context`) and to use `abs` instead of `square` to
avoid deprecated bool ops.
22f67b5958