[Frontend] Treat .cuh files as CUDA source files

to synchronize with tools/clang-format/git-clang-format

tra: Keeping them in sync does have a minor benefit of not raising a question why the two maps are different.

Differential Revision: https://reviews.llvm.org/D91034

clang/lib/Frontend/FrontendOptions.cpp

@@ -29,7 +29,7 @@ InputKind FrontendOptions::getInputKindForExtension(StringRef Extension) {
       .Case("cppm", Language::CXX)
       .Case("iim", InputKind(Language::CXX).getPreprocessed())
       .Case("cl", Language::OpenCL)
-      .Case("cu", Language::CUDA)
+      .Cases("cu", "cuh", Language::CUDA)
       .Case("hip", Language::HIP)
       .Cases("ll", "bc", Language::LLVM_IR)
       .Default(Language::Unknown);

clang/test/Parser/cuda-check-input-kind-assoc.cuh

@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -fsyntax-only -Werror %s
+
+// Check input kind association for cuh extension.
+
+__attribute__((host, device)) void hd_fn() {}