In commit 835f3494 (Help: Update cmake-buildsystem(7) build and usage
requirements, 2024-04-23) we labeled the sections documenting `COMPILE_*`
properties as "build properties".  All the properties it documents are
about compilation steps before linking, including the Autogen features
for compiling Qt metadata, so rename the sections as "compile properties".
This is also consistent with the name of the `$<COMPILE_ONLY:...>`
generator expression.