llvm5.0: use input kind helper to avoid breakage

Upstream llvm renamed an enum, so use a helper function that is
available in all versions to fix compatibility.
Signed-off-by: Brenden Blanco <bblanco@gmail.com>

src/cc/frontends/clang/loader.cc

@@ -230,8 +230,8 @@ int ClangLoader::parse(unique_ptr<llvm::Module> *mod, TableStorage &ts, const st
   if (in_memory) {
     invocation0.getPreprocessorOpts().addRemappedFile(main_path, &*main_buf);
     invocation0.getFrontendOpts().Inputs.clear();
-    invocation0.getFrontendOpts().Inputs.push_back(
-        FrontendInputFile(main_path, IK_C));
+    invocation0.getFrontendOpts().Inputs.push_back(FrontendInputFile(
+        main_path, FrontendOptions::getInputKindForExtension("c")));
   }
   invocation0.getFrontendOpts().DisableFree = false;
 
@@ -260,8 +260,8 @@ int ClangLoader::parse(unique_ptr<llvm::Module> *mod, TableStorage &ts, const st
     invocation1.getPreprocessorOpts().addRemappedFile(f.first, &*f.second);
   invocation1.getPreprocessorOpts().addRemappedFile(main_path, &*out_buf);
   invocation1.getFrontendOpts().Inputs.clear();
-  invocation1.getFrontendOpts().Inputs.push_back(
-      FrontendInputFile(main_path, IK_C));
+  invocation1.getFrontendOpts().Inputs.push_back(FrontendInputFile(
+      main_path, FrontendOptions::getInputKindForExtension("c")));
   invocation1.getFrontendOpts().DisableFree = false;
 
   compiler1.createDiagnostics();
@@ -286,8 +286,8 @@ int ClangLoader::parse(unique_ptr<llvm::Module> *mod, TableStorage &ts, const st
     invocation2.getPreprocessorOpts().addRemappedFile(f.first, &*f.second);
   invocation2.getPreprocessorOpts().addRemappedFile(main_path, &*out_buf1);
   invocation2.getFrontendOpts().Inputs.clear();
-  invocation2.getFrontendOpts().Inputs.push_back(
-      FrontendInputFile(main_path, IK_C));
+  invocation2.getFrontendOpts().Inputs.push_back(FrontendInputFile(
+      main_path, FrontendOptions::getInputKindForExtension("c")));
   invocation2.getFrontendOpts().DisableFree = false;
   // Resort to normal inlining. In -O0 the default is OnlyAlwaysInlining and
   // clang might add noinline attribute even for functions with inline hint.