To reland https://github.com/llvm/llvm-project/pull/124846, we need to
make symbolizer consistent with the case when line number is 0. Always
using filename and line from debug info even if the line number is 0
sounds like the reasonable path to go.

Currently, `DIContext::getLineInfoForAddress` and
`DIContext::getLineInfoForDataAddress` returns empty DILineInfo when the
debug info is missing for the given address. This is not differentiable
with the case when debug info is found for the given address but the
debug info is default value (filename:linenum is <invalid>:0).

This change wraps the return types of `DIContext::getLineInfoForAddress`
and `DIContext::getLineInfoForDataAddress` with `std::optional`.

Identified with misc-include-cleaner.

I'm planning to remove StringRef::equals in favor of
StringRef::operator==.

- StringRef::operator==/!= outnumber StringRef::equals by a factor of
  53 under llvm/ in terms of their usage.

- The elimination of StringRef::equals brings StringRef closer to
  std::string_view, which has operator== but not equals.

- S == "foo" is more readable than S.equals("foo"), especially for
  !Long.Expression.equals("str") vs Long.Expression != "str".

GNU addr2line supports lookup by symbol name in addition to the existing
address lookup. llvm-symbolizer starting from
e144ae54dcb96838a6176fd9eef21028935ccd4f supports lookup by symbol name.
This change extends this lookup with possibility to specify optional
offset.

Now the address for which source information is searched for can be
specified with offset:

    llvm-symbolize --obj=abc.so "SYMBOL func_22+0x12"

It decreases the gap in features of llvm-symbolizer and GNU addr2line.
This lookup now is supported for code only.

Migrated from: https://reviews.llvm.org/D139859
Pull request: https://github.com/llvm/llvm-project/pull/75067

Recent versions of GNU binutils starting from 2.39 support symbol+offset
lookup in addition to the usual numeric address lookup. This change adds
symbol lookup to llvm-symbolize and llvm-addr2line.

Now llvm-symbolize behaves closer to GNU addr2line, - if the value specified
as address in command line or input stream is not a number, it is treated as
a symbol name. For example:

    llvm-symbolize --obj=abc.so func_22
    llvm-symbolize --obj=abc.so "CODE func_22"

This lookup is now supported only for functions. Specification with
offset is not supported yet.

This is a recommit of 2b27948783e4bbc1132d3220d8517ef62607b558, reverted
in 39fec5457c0925bd39f67f63fe17391584e08258 because the test
llvm/test/Support/interrupts.test started failing on Windows. The test was
changed in 18f036d0105589c3175bb51a518c5d272dae61e2 and is also updated in
this commit.

Differential Revision: https://reviews.llvm.org/D149759

This reverts commit 2b27948783e4bbc1132d3220d8517ef62607b558.
On some buildbots the test LLVM::interrupts.test start failing.

Recent versions of GNU binutils starting from 2.39 support symbol+offset
lookup in addition to the usual numeric address lookup. This change adds
symbol lookup to llvm-symbolize and llvm-addr2line.

Now llvm-symbolize behaves closer to GNU addr2line, - if the value specified
as address in command line or input stream is not a number, it is treated as
a symbol name. For example:

    llvm-symbolize --obj=abc.so func_22
    llvm-symbolize --obj=abc.so "CODE func_22"

This lookup is now supported only for functions. Specification with
offset is not supported yet.

Differential Revision: https://reviews.llvm.org/D149759

I also ran `git clang-format` to get the headers in the right order for
the new location, which has changed the order of other headers in two
files.