[CMake][Fuchsia] Disable terminfo database in Fuchsia toolchain

It's used to determine whether terminal supports colors, but within LLVM
it's only used in handful of places and in Clang it's only used in AST
dumper, otherwise Clang relies on the -fcolor-diagnostics flag which we
pass explicitly from our build system anyway. This eliminates one of the
shared libraries dependencies making the toolchain less reliant on the
host environment.

Differential Revision: https://reviews.llvm.org/D40329

llvm-svn: 319088