[llvm] llvm_gtest: Only install once (PR #96959)

[Tom Stellard via llvm-commits]

tstellar wrote:

> Hmm, what installs the libraries after this change?

The add_llvm_library calls are generating the install targets.

> Is that what this addresses? Thanks!

Yes, and there was also a bug where if you configure with `-DCMAKE_INSTALL_PREFIX` and without `-DLLVM_LIBDIR_SUFFIX` then you end up with the libraries installed into two locations, because add_llvm_library installs to `lib${LLVM_LIBDIR_SUFFIX} and the custom insall targets removed in this patch install to `CMAKE_INSTALL_LIBDIR` which is different in this scenario.


https://github.com/llvm/llvm-project/pull/96959