lld: Make a test not fail if "repro" is part of the build directory name
r268231 made it so that the name of the --reproduce archive
is no longer listed in the response file. Previously, with
"--reproduce repro.tar" the response file would contain
but after that change it contained
instead. The test added for this in r268231 checked that
the response file doesn't contain the string "repro", but
if the build dir is named e.g. "llvm-build-repro" then the
test fails because of that.
Change the assert to check that "repro" doesn't exist at the
beginning of the line instead. I verified that the test
still fails with r268231 reverted.
The test technically still fails if someone builds llvm in a directory
'/repro' below the root directory. Don't do that :)