CMake: do not expand variables beforehand
Fixes:
CMake Error at webenginepart/src/CMakeLists.txt:113 (if):
if given arguments:
"(" "NOT" "0" ")" "AND"
Unknown arguments specified
See also: https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/267
Signed-off-by: Andreas Sturmlechner asturm@gentoo.org