[ELF][Writer] Don't infinite loop.

This will be tested by a following committ that runs the linker
with no inputs.

llvm-svn: 171576
diff --git a/lld/lib/ReaderWriter/ELF/WriterELF.cpp b/lld/lib/ReaderWriter/ELF/WriterELF.cpp
index 7907f3f..fed76362 100644
--- a/lld/lib/ReaderWriter/ELF/WriterELF.cpp
+++ b/lld/lib/ReaderWriter/ELF/WriterELF.cpp
@@ -1755,7 +1755,7 @@
       _programHeader->setFileOffset(_elfHeader->fileSize());
     }
     bool newSegmentHeaderAdded = true;
-    while (true) {
+    while (true && !_segments.empty()) {
       for (auto si : _segments) {
         newSegmentHeaderAdded = _programHeader->addSegment(si);
         numSlices += si->numSlices();