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.
Followup to #76804. Fixes#144646.
Signed-off-by: Anders Kaseorg <andersk@mit.edu>
e12f4db556