[debuginfo][coro] Emit debug info labels for coroutine resume points (#141937)

RFC on discourse:
https://discourse.llvm.org/t/rfc-debug-info-for-coroutine-suspension-locations-take-2/86606

With this commit, we add `DILabel` debug infos to the resume points of a
coroutine. Those labels can be used by debugging scripts to figure out
the exact line and column at which a coroutine was suspended by looking
up current `__coro_index` value inside the coroutines frame, and then
searching for the corresponding label inside the coroutine's resume
function.

The DWARF information generated for such a label looks like:

```
0x00000f71:     DW_TAG_label
                  DW_AT_name    ("__coro_resume_1")
                  DW_AT_decl_file       ("generator-example.cpp")
                  DW_AT_decl_line       (5)
                  DW_AT_decl_column     (3)
                  DW_AT_artificial      (true)
                  DW_AT_LLVM_coro_suspend_idx   (0x01)
                  DW_AT_low_pc  (0x00000000000019be)
```

The labels can be mapped to their corresponding `__coro_idx` values
either via their naming convention `__coro_resume_<N>` or using the new
`DW_AT_LLVM_coro_suspend_idx` attribute. In gdb, those line numebrs can
be looked up using `info line -function my_coroutine -label
__coro_resume_1`. LLDB unfortunately does not understand DW_TAG_label
debug information, yet.

Given this is an artificial compiler-generated label, I did apply the
DW_AT_artificial tag to it. The DWARFv5 standard only allows that tag on
type and variable definitions, but this is a natural extension and was
also blessed in the RFC on discourse.

Also, this commit adds `DW_AT_decl_column` to labels, not only for
coroutines but also for normal C and C++ labels. While not strictly
necessary, I am doing so now because it would be harder to do so later
without breaking the binary LLVM-IR format

Drive-by fixes: While reading the existing test cases to understand how
to write my own test case, I did a couple of small typo fixes and
comment improvements

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/IR/DIBuilder.cpp b/llvm/lib/IR/DIBuilder.cpp
index a542695..1344df9 100644
--- a/llvm/lib/IR/DIBuilder.cpp
+++ b/llvm/lib/IR/DIBuilder.cpp
@@ -946,9 +946,13 @@ DILocalVariable *DIBuilder::createParameterVariable(
 }
 
 DILabel *DIBuilder::createLabel(DIScope *Context, StringRef Name, DIFile *File,
-                                 unsigned LineNo, bool AlwaysPreserve) {
+                                unsigned LineNo, unsigned Column,
+                                bool IsArtificial,
+                                std::optional<unsigned> CoroSuspendIdx,
+                                bool AlwaysPreserve) {
   auto *Scope = cast<DILocalScope>(Context);
-  auto *Node = DILabel::get(VMContext, Scope, Name, File, LineNo);
+  auto *Node = DILabel::get(VMContext, Scope, Name, File, LineNo, Column,
+                            IsArtificial, CoroSuspendIdx);
 
   if (AlwaysPreserve) {
     /// The optimizer may remove labels. If there is an interest