Overriding CMAKE_INSTALL_PREFIX is bad practice

[patbrandt]

fmi-library/CMakeLists.txt

Line 88 in 998768c

SET(CMAKE_INSTALL_PREFIX ${FMILIB_INSTALL_PREFIX} CACHE INTERNAL "Prefix prepended to install directories" FORCE)

Though calling it "practice" implies that I've ever seen it done elsewhere. This is silently and forcibly(!) setting a core cmake option to something other than what the user might specify, which is not great. In isolation to one project (this one), it's... probably fine? When building code with/against FMILibrary it blows up.

We are attempting to use FMILibrary as a sub-project, and this line nukes the install path for the rest of our code, unless we set the FMI-specific install path to the same one. Which, to be fair, we probably would, but it's a pit that we easily fell into.

My recommendation would be to simply use CMAKE_INSTALL_PREFIX natively, but at the very least don't override user settings for standard cmake variables.

[jschueller]

this can be closed @modelonrobinandersson