Downstream cmake integration fails to find `fmt`

[boschmitt]

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Describe the bug

When trying to create a downstream project with CUDAQ cmake integration, the configuration step fails to find the fmt library required by CUDAQ.

The issue is that fmt honors CMAKE_INSTALL_LIBDIR while CUDAQ does not. Hence, on certain systems, installing CUDAQ will end up placing the required fmt in lib64/ instead of lib/. CUDAQ cmake modules will fail to find it as it looks for it in lib/. (It is unclear at this point if this could affect other scenarios, i.e., not only downstream integration.)

Steps to reproduce the bug

Follow the docs on a system where CMAKE_INSTALL_LIBDIR is lib64.

Expected behavior

Correctly find fmt in the downstream cmake integration.

Is this a regression? If it is, put the last known working version (or commit) here.

Not a regression

Environment

• CUDA Quantum version: nvq++ Version proto-0.8.0 (https://github.com/NVIDIA/cuda-quantum 6016e2f23216b64f0fca083bef22fb8266ea9049)
• Operating system: Linux fedora 6.8.9-200.fc39.x86_64

Suggestions

We should honor CMAKE_INSTALL_LIBDIR and change all hardcoded lib in the building system. Alternatively, we could force CMAKE_INSTALL_LIBDIR to lib in our main configuration file or change the downstream integration to look for fmt in the correct location (based on CMAKE_INSTALL_LIBDIR.