Since a while I know the problem with the webkit under Manjaro also and solved it in the past just like alen.
In the past, the compilation took more time because additional debug messages were displayed. Later on, the
build script was apparently modified and debug messages were turned off. This made the compilation faster
again, but because webkit is very complex, it still takes several hours.
Since an update for the webkit library is available recently, the library from the AUR does not work anymore,
because the required dependency (enchant) from the repository is too old.
With a report in the forum I have waited, hoping that the enchant-library will be updated soon and the build
script will run again without errors.
However, the libraries from AUR were not a permanent solution, because it was already pointed out when
compiling that the outdated library should not be used because of the many security vulnerabilities.
On the following pages there is a pinned comment that seems to describe a solution, but for security reasons
I don't want to try it:
https://aur.archlinux.org/packages/webkitgtkhttps://aur.archlinux.org/packages/webkitgtk2