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. (See #67234, for
example.) Fix this throughout the tree.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
