swr/rast: Fix WriteBitcodeToFile usage with llvm-7.0.

Fix build error after llvm-7.0svn r325155 ("Pass a reference to a module
to the bitcode writer.").

  CXX      rasterizer/jitter/libmesaswr_la-JitManager.lo
rasterizer/jitter/JitManager.cpp:548:30: error: reference to type 'const llvm::Module' could not bind to an lvalue of type 'const llvm::Module *'
    llvm::WriteBitcodeToFile(M, bitcodeStream);
                             ^

Suggested-by: George Kyriazis <george.kyriazis@intel.com>
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-By: George Kyriazis <george.kyriazis@intel.com>

src/gallium/drivers/swr/rasterizer/jitter/JitManager.cpp

@@ -545,7 +545,11 @@ static inline uint32_t ComputeModuleCRC(const llvm::Module* M)
     std::string bitcodeBuffer;
     raw_string_ostream bitcodeStream(bitcodeBuffer);
 
+#if LLVM_VERSION_MAJOR >= 7
+    llvm::WriteBitcodeToFile(*M, bitcodeStream);
+#else
     llvm::WriteBitcodeToFile(M, bitcodeStream);
+#endif
     //M->print(bitcodeStream, nullptr, false);
 
     bitcodeStream.flush();