We've made several attempts to add a dummy symbol to `mocs_compilation.cpp`
when there are no automoc sources:

* commit 4a9daae4 (automoc: silence linker warning on macos,
                     2022-05-25, v3.24.0-rc1~55^2)
* commit 844244cc (automoc: avoid compiler warnings in linker-warning-
                     silencing code, 2022-08-10, v3.24.1~6^2)
* commit fc862838 (automoc: avoid more compiler warnings in linker-
                     warning-silencing code, 2022-08-29)

The last attempt derives a symbol name from the path to the source
file, but that breaks reproducible builds because it is not stable
w.r.t. the location of the build tree.  Revert all these attempts
for the 3.24 release series, and return to what 3.23 and below did.
Further investigation will be needed to resolve the original issue.

Fixes: #23937
Issue: #23551, #23823, #23823