[DOC] Add a guide to update SYCL device library

docs/update_sycl_libdevice.md

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+# Guide to Update SYCL Device Library
+
+This guide will walk you through the steps to update the SYCL device library using the Intel DPC++ compiler.
+
+## Step 1: Display Commands used during Compilation Process
+1. Open a terminal.
+2. Run the following command to compile a C++ file:
+```sh
+dpcpp -save-temps -#x t.cpp
+```
+Replace t.cpp with any C++ file of your choice. This command will display the commands used during the compilation process.
+
+## Step 2: Locate the llvm-link Command
+From the output of the previous command, find the llvm-link command line. It should look similar to the following example:
+```sh
+"/opt/intel/oneapi/compiler/2025.0/bin/compiler/llvm-link" \
+    -only-needed \
+    t-sycl-spir64-unknown-unknown-b331ea.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-crt.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-complex.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-complex-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-cmath.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-cmath-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf-bf16.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cassert.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cstring.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-complex.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-complex-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cmath.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cmath-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf-bf16.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-user-wrappers.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-compiler-wrappers.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-stubs.bc \
+    -o \
+    t-sycl-spir64-unknown-unknown-d81f68.bc \
+    --suppress-warnings
+```
+
+## Step 3: Modify the llvm-link Command
+Remove the `-only-needed` option and the intermediate file `t-sycl-spir64-unknown-unknown-b331ea.bc` from the command line.
+And modify to output file name to `libsycl-spir64-unknown-unknown.bc`.
+The modified command should look like this:
+```sh
+"/opt/intel/oneapi/compiler/2025.0/bin/compiler/llvm-link" \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-crt.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-complex.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-complex-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-cmath.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-cmath-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-imf-bf16.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cassert.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cstring.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-complex.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-complex-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cmath.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-cmath-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf-fp64.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-fallback-imf-bf16.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-user-wrappers.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-compiler-wrappers.bc \
+    /opt/intel/oneapi/compiler/2025.0/bin/compiler/../../lib/libsycl-itt-stubs.bc \
+    -o \
+    libsycl-spir64-unknown-unknown.bc \
+    --suppress-warnings
+```
+
+## Step 4: Execute the Modified Command
+Copy the modified llvm-link command.
+Paste and run it in the terminal.
+
+## Step 5: Check for Manual Changes
+Check the log of the existing device library to see what manual changes need to be made:
+```sh
+git log third_party/intel/backend/lib/libsycl-spir64-unknown-unknown.bc
+```
+Look for any specific changes mentioned in the commit messages. For example, from commit 0dd37fc92c46f35c6ced34801e51058b6b89ea47, you need to change one of the module metadata from 4 to 3.
+
+## Step 6: Apply Manual Changes
+`llvm-dis` to disassemble the bitcode library, then based on the information from the git log, apply the necessary manual changes to the updated device library.
+Reassemble the modified LLVMIR device library using `llvm-as`.
+
+By following these steps, you will have successfully updated the SYCL device library and applied any necessary manual changes.