swift234

[test] Check LD_LIBRARY_PATH a little less strictly.

LD_LIBRARY_PATH is one of the few environment variables the LLVM 'lit'
tool /doesn't/ strip out, presumably because on some Linux systems
it's necessary to run some of the built products being tested.
However, the Swift driver also uses LD_LIBRARY_PATH when providing -L
options to the script interpreter on Linux. Weaken some of our tests
when there's an LD_LIBRARY_PATH in the environment.

(There are similar environment variables on OS X, but we don't have to
do anything special there because lit /does/ strip those out. This is
presumably okay because all of LLVM's load-time dependencies on OS X
are in standard system locations.)

https://bugs.swift.org/browse/SR-813