swr: Fix build with llvm-10.0.

swr: Fix build with llvm-10.0.

Fix build error after llvm-10.0 commit 1dfede3122ee ("Move
CodeGenFileType enum to Support/CodeGen.h").

../src/gallium/drivers/swr/rasterizer/jitter/JitManager.cpp: In member function ‘void JitManager::DumpAsm(llvm::Function*, const char*)’:
../src/gallium/drivers/swr/rasterizer/jitter/JitManager.cpp:428:45: error: ‘CGFT_AssemblyFile’ is not a member of ‘llvm::TargetMachine’
             *pMPasses, filestream, nullptr, TargetMachine::CGFT_AssemblyFile);
                                             ^

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Jan Zielinski <jan.zielinski@intel.com>