[LLDB] Fix script to work with GNU sed
[LLDB] Fix script to work with GNU sed

GNU sed and BSD sed have a different command-line syntax for in-place
editing, and the current form of the script would only work with BSD
sed. The easiest way to get cross-platform behavior is to specify a
backup suffix and then just delete the backup file at the end. (BSD sed
is the default on macOS, but it's possible to acquire GNU coreutils and
have your `sed` be GNU sed even on macOS; I'm aware it's not officially
supported in any capacity, but it's easy enough to support here.)

An alternative would be using `perl -p -i -e` instead of `sed -i`, but I
figured it was best to make the minimal working change.

Differential Revision: https://reviews.llvm.org/D51374

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@340885 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb