[clang] [Driver][SYCL] Error on C inputs when compiling with -fsycl (PR #200318)

[Michael Toguchi via cfe-commits]

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@@ -0,0 +1,7 @@
+// Verify that a .c file compiled with -fsycl is an error.
+// RUN: not %clang -### -fsycl %s 2>&1 | FileCheck -check-prefix ERR %s
+// ERR: error: invalid argument '{{.*}}sycl-c-warn.c' not allowed with '-fsycl'
+
+// Verify that explicitly forcing -x c with -fsycl is also an error.
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mdtoguchi wrote:

I wouldn't expect the ability to capture this behavior with the `-cc1` command line be useful.  If the user is already using `-cc1` directly, any issues with expected source type would be pretty low on the totem pole for useful functionality when involving `-fsycl`.

https://github.com/llvm/llvm-project/pull/200318