Prepend RPATH of install/build directories to AM_LDFLAGS

Description

• Prevent being overridden by other libraries or environment (e.g. the LDFLAGS set by the default Conda environment at CIT).
• top-level and *:pkg CI jobs now test building in environment with LDFLAGS=/usr/lib64 and LALSuite packages installed in /usr/lib64.
• Add installcheck tests of the lal*_version executables; check that these are reporting the correct information, an error would indicate linking against the wrong libraries. (This is easier than directly probing with ldd which libraries are linked to, as that would involve more platform-specific code, e.g. ldd vs otool.)

Closes #633

API Changes and Justification

Backwards Compatible Changes

• This change does not modify any class/function/struct/type definitions in a public C header file or any Python class/function definitions
• This change adds new classes/functions/structs/types to a public C header file or Python module

Backwards Incompatible Changes

• This change modifies an existing class/function/struct/type definition in a public C header file or Python module
• This change removes an existing class/function/struct/type from a public C header file or Python module

If any of the Backwards Incompatible check boxes are ticked please provide a justification why this change is necessary and why it needs to be done in a backwards incompatible way.

Review Status

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