BINARY_PATH Fix, master branch (2021.07.03.)

Fixed the handling of <FOO>_BINARY_PATH in lcg_external_module(...), after debugging the issue in athena!44893 (merged).

In the previous implementation repeated calls to find_package(...) in the same context would lead to <FOO>_BINARY_PATH growing and growing, ever being extended by $<BUILD_INTERFACE:...> and $<INSTALL_INTERFACE:...> generator expressions.

I now changed the code to behave in the way in which lcg_external_python_module(...) has been operating for a long time. Introducing the internal _<FOO>_BINARY_PATH variable, which clients should not really have to know about.

@fwinkl, I'm afraid that athena!44893 (merged) will have to be put on hold until this update reaches the nightly.

mentioned in merge request athena!44893 (merged)

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #511]

mentioned in commit 0386f5ed

merged