[clang-tools-extra] [Docs][LTO] Updated HowToSubmitABug.rst for LTO crashes (PR #68389)

[Matheus Izvekov via cfe-commits]

================
@@ -153,6 +153,67 @@ Please run this, then file a bug with the instructions and reduced .bc file
 that bugpoint emits.  If something goes wrong with bugpoint, please submit
 the "foo.bc" file and the option that llc crashes with.
 
+LTO bugs
+---------------------------
+
+If you encounter a bug that leads to crashes in the LLVM LTO phase when using
+the `-flto` option, follow these steps to diagnose and report the issue:
+
+Compile your source file to a .bc (Bitcode) file with the following flags,
+in addition to your existing compilation options:
+
+.. code-block:: bash
+
+   export CFLAGS="-flto -fuse-ld=lld" CXXFLAGS="-flto -fuse-ld=lld" LDFLAGS="-Wl,-plugin-opt=save-temps"
+
+These flags enable LTO and save temporary files generated during compilation
+for later analysis.
+
+On Windows, you should use lld-link as the linker. Adjust your compilation 
+flags as follows:
+
+.. code-block:: bash
+
+   export CFLAGS="-flto -fuse-ld=lld-link" CXXFLAGS="-flto -fuse-ld=lld-link" LDFLAGS="-Wl,-plugin-opt=save-temps"
----------------
mizvekov wrote:

```suggestion
On Windows, you should be using lld-link as the linker. Adjust your compilation 
flags as follows:
* Add `/lldsavetemps` to the linker flags.
* When linking from the compiler driver, Add `/link /lldsavetemps` in order to forward that flag to the linker.

https://github.com/llvm/llvm-project/pull/68389