shake.h not compatible for the NaCl GCC compiler

[asbai]

crypto++ 8.1: shake.h

The Google Native Client compiler complain something like: "SHACK128: there is no field named SHAKE_Final", we must use the full template name to fix it:

// ...
SHAKE128(unsigned int outputSize) : SHAKE_Final<128>(outputSize) {} // NaCl compiler fix
// ...
SHAKE256(unsigned int outputSize) : SHAKE_Final<256>(outputSize) {} // NaCl compiler fix

[noloader]

Also see Issue 818 and Commit fc3b16e3a39d.