[polly] Drop nonexistant LLVM_PLUGIN_EXPORT macro from llvmGetPassPluginInfo()

Fixes build:
/build/polly/lib/Support/RegisterPasses.cpp:709:80: error: expected ';' after top level declarator
extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK LLVM_PLUGIN_EXPORT
                                                                               ^
                                                                              ;

Was missed in rL332796 / D47082

llvm-svn: 332814

Author: LebedevRI

polly/lib/Support/RegisterPasses.cpp

@@ -706,7 +706,7 @@ void RegisterPollyPasses(PassBuilder &PB) {
 } // namespace polly
 
 // Plugin Entrypoint:
-extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK LLVM_PLUGIN_EXPORT
+extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK
 llvmGetPassPluginInfo() {
   return {LLVM_PLUGIN_API_VERSION, "Polly", LLVM_VERSION_STRING,
           polly::RegisterPollyPasses};