Build shared libraries by default?

[sebproell]

Arising from #809 and #829, I propose to make a shared library build the default setting in CMake. This means you need to specifically request FOUR_C_BUILD_SHARED_LIBS =OFF for a static library build. I am proposing this since I would personally always use a shared library build. WDYT?

Relevant comment: #829 (comment)

[davidrudlstorfer]

Sounds good 👌

Based on the performance comparison from last year: would it make sense to turn of the shared library build for the clusters? Most of the times memory is not a problem there and the performance plays a bigger role on the clusters.

[sebproell]

First, this is a user decision. I am talking about the default that we set if users don't say anything about it. Second, I interpreted the performance data to tell me there is no difference.