Rollup merge of #72625 - Amanieu:asm-srcloc, r=petrochenkov

Improve inline asm error diagnostics

Previously we were just using the raw LLVM error output (with line, caret, etc) as the diagnostic message, which ends up looking rather out of place with our existing diagnostics.

The new diagnostics properly format the diagnostics and also take advantage of LLVM's per-line `srcloc` attribute to map an error in inline assembly directly to the relevant line of source code.

Incidentally also fixes #71639 by disabling `srcloc` metadata during LTO builds since we don't know what crate it might have come from. We can only resolve `srcloc`s from the currently crate since it indexes into the source map for the current crate.

Fixes #72664
Fixes #71639

r? @petrochenkov

### Old style

```rust
#![feature(llvm_asm)]

fn main() {
    unsafe {
        let _x: i32;
        llvm_asm!(
            "mov $0, $1
             invalid_instruction $0, $1
             mov $0, $1"
             : "=&r" (_x)
             : "r" (0)
             :: "intel"
        );
    }
}
```

```
error: <inline asm>:3:14: error: invalid instruction mnemonic 'invalid_instruction'
             invalid_instruction ecx, eax
             ^~~~~~~~~~~~~~~~~~~

  --> src/main.rs:6:9
   |
6  | /         llvm_asm!(
7  | |             "mov $0, $1
8  | |              invalid_instruction $0, $1
9  | |              mov $0, $1"
...  |
12 | |              :: "intel"
13 | |         );
   | |__________^
```

### New style

```rust
#![feature(asm)]

fn main() {
    unsafe {
        asm!(
            "mov {0}, {1}
             invalid_instruction {0}, {1}
             mov {0}, {1}",
            out(reg) _,
            in(reg) 0i64,
        );
    }
}
```

```
error: invalid instruction mnemonic 'invalid_instruction'
 --> test.rs:7:14
  |
7 |              invalid_instruction {0}, {1}
  |              ^
  |
note: instantiated into assembly here
 --> <inline asm>:3:14
  |
3 |              invalid_instruction rax, rcx
  |              ^^^^^^^^^^^^^^^^^^^
```

1 files changed, 27 insertions, 4 deletions

diff --git a/src/rustllvm/RustWrapper.cpp b/src/rustllvm/RustWrapper.cpp
index 24f35627d10..6fac2662506 100644
--- a/src/rustllvm/RustWrapper.cpp
+++ b/src/rustllvm/RustWrapper.cpp
@@ -1216,10 +1216,33 @@ extern "C" void LLVMRustSetInlineAsmDiagnosticHandler(
   unwrap(C)->setInlineAsmDiagnosticHandler(H, CX);
 }
 
-extern "C" void LLVMRustWriteSMDiagnosticToString(LLVMSMDiagnosticRef D,
-                                                  RustStringRef Str) {
-  RawRustStringOstream OS(Str);
-  unwrap(D)->print("", OS);
+extern "C" bool LLVMRustUnpackSMDiagnostic(LLVMSMDiagnosticRef DRef,
+                                           RustStringRef MessageOut,
+                                           RustStringRef BufferOut,
+                                           unsigned* LocOut,
+                                           unsigned* RangesOut,
+                                           size_t* NumRanges) {
+  SMDiagnostic& D = *unwrap(DRef);
+  RawRustStringOstream MessageOS(MessageOut);
+  MessageOS << D.getMessage();
+
+  if (D.getLoc() == SMLoc())
+    return false;
+
+  const SourceMgr &LSM = *D.getSourceMgr();
+  const MemoryBuffer *LBuf = LSM.getMemoryBuffer(LSM.FindBufferContainingLoc(D.getLoc()));
+  LLVMRustStringWriteImpl(BufferOut, LBuf->getBufferStart(), LBuf->getBufferSize());
+
+  *LocOut = D.getLoc().getPointer() - LBuf->getBufferStart();
+
+  *NumRanges = std::min(*NumRanges, D.getRanges().size());
+  size_t LineStart = *LocOut - (size_t)D.getColumnNo();
+  for (size_t i = 0; i < *NumRanges; i++) {
+    RangesOut[i * 2] = LineStart + D.getRanges()[i].first;
+    RangesOut[i * 2 + 1] = LineStart + D.getRanges()[i].second;
+  }
+
+  return true;
 }
 
 extern "C" LLVMValueRef LLVMRustBuildCleanupPad(LLVMBuilderRef B,