CMakeLists.txt: Don't use '${}' with variables in if-clauses. Variable...

CMakeLists.txt: Don't use '${}' with variables in if-clauses. Variable expansion in if-clauses works without it.

The '${}' can lead to unwanted side-effects, so better not use it. . See: https://cmake.org/cmake/help/latest/command/if.html#variable-expansion