[clang] [Clang][CodeGen] Emit “trap reasons” on UBSan traps (PR #145967)

[Michael Buch via cfe-commits]

Michael137 wrote:

Yea I think what we need is to just set the current DebugLocation. We usually do this using `ApplyDebugLocation::CreateArtificial` so that the artificial function we're generating has some artificial debug-location.

When I do this in `EmitCfiCheckFail` the crash disappears and we generate reasonable looking debug-info:
```
0x00000061:   DW_TAG_subprogram
                DW_AT_name      ("__clang_trap_msg$Undefined Behavior Sanitizer$Control flow integrity check failed")
                DW_AT_artificial        (true)
                DW_AT_external  (true)
                DW_AT_inline    (DW_INL_inlined)

0x00000067:   DW_TAG_subprogram
                DW_AT_low_pc    (0x0000000000000000)
                DW_AT_high_pc   (0x0000000000000043)
                DW_AT_frame_base        (DW_OP_reg7 RSP)
                DW_AT_linkage_name      ("__cfi_check_fail")
                DW_AT_artificial        (true)
                DW_AT_external  (true)

0x0000007a:     DW_TAG_formal_parameter
                  DW_AT_location        (DW_OP_reg5 RDI)
                  DW_AT_type    (0x0000009a "void *")
                  DW_AT_artificial      (true)

0x00000081:     DW_TAG_formal_parameter
                  DW_AT_location        (DW_OP_reg4 RSI)
                  DW_AT_type    (0x0000009a "void *")
                  DW_AT_artificial      (true)

0x00000088:     DW_TAG_inlined_subroutine
                  DW_AT_abstract_origin (0x00000061 "__clang_trap_msg$Undefined Behavior Sanitizer$Control flow integrity check failed")
                  DW_AT_ranges  (0x00000030
                     [0x0000000000000029, 0x0000000000000033)
                     [0x000000000000003e, 0x0000000000000043))
                  DW_AT_call_file       ("clang/test/CodeGen/<stdin>")
                  DW_AT_call_line       (0)

0x00000093:     NULL
```

I.e., the artificial ubsan trap frame is inlined into `__cfi_check_fail`. We should probably follow-up on how this looks in LLDB. But off the top I think this should Just Work.

https://github.com/llvm/llvm-project/pull/145967