[LLD] - Do not crash when reporting errors when .debug_line_str (DWARF5) is used

[LLD] - Do not crash when reporting errors when .debug_line_str (DWARF5) is used

Imagine we have the following code:

int foo();
int main() { return foo(); }

It will crash if you try to compile it with
`clang -O0 -gdwarf-5 test.cpp -o test -g -fuse-ld=lld`

The crash happens inside the LLVM DWARF parser because LLD does not provide
the .debug_line_str section. At the same time for correct parsing and reporting,
we anyways need to provide this section from our side.

The patch fixes the issue.

llvm-svn: 343667