Since the setting DCMAKE_SKIP_BUILD_RPATH was disabled, we can now run
the checkPhase of cmake derivations without having to tweak the
LD_LIBRARY_PATH anymore.
Naive concatenation of $LD_LIBRARY_PATH can result in an empty
colon-delimited segment; this tells glibc to load libraries from the
current directory, which is definitely wrong, and may be a security
vulnerability if the current directory is untrusted. This particular
case probably has no security relevance, but we should avoid this
unsafe pattern anyway in case it gets copied. See #76804.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
