Use posix_fallocate instead of ftruncate.

This makes sure that space is actually available. With this change
running lld on a full file system causes it to exit with

failed to open foo: No space left on device

instead of crashing with a sigbus.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276017 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed