Update installation.md

Had to change the LLVM cmake command for it to work.

Author: skrobchik

src/offload/installation.md

@@ -30,7 +30,7 @@ git clone [email protected]:llvm/llvm-project
 cd llvm-project
 mkdir build
 cd build
-cmake -G Ninja ../llvm -DLLVM_TARGETS_TO_BUILD="host,AMDGPU,NVPTX" -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_RUNTIMES="offload,openmp" -DLLVM_ENABLE_PLUGINS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=.
+cmake -G Ninja ../llvm -DLLVM_TARGETS_TO_BUILD="host" -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="AMDGPU;NVPTX" -DLLVM_ENABLE_ASSERTIONS=ON -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_ENABLE_RUNTIMES="offload;openmp" -DLLVM_ENABLE_PLUGINS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=.
 ninja
 ninja install
 ```