Refactor pragma handling (pass everything to LLVM)

Change-Id: Id09d4934af06f0880cd867456218602ce9a9e2de
diff --git a/slang_rs_backend.cpp b/slang_rs_backend.cpp
index 67f2406..0d9c2d4 100644
--- a/slang_rs_backend.cpp
+++ b/slang_rs_backend.cpp
@@ -44,7 +44,7 @@
                      clang::Diagnostic *Diags,
                      const clang::CodeGenOptions &CodeGenOpts,
                      const clang::TargetOptions &TargetOpts,
-                     const PragmaList &Pragmas,
+                     PragmaList *Pragmas,
                      llvm::raw_ostream *OS,
                      Slang::OutputType OT,
                      clang::SourceManager &SourceMgr,