[SYCL][NFC] Fix RUN-line in no-prototype-func.c test (#2059)

Updated run line to avoid leaving no-prototype-func.ll file in source
directory after test run.

Author: Fznamznon

clang/test/SemaSYCL/no-prototype-func.c

@@ -1,3 +1,3 @@
-// RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -emit-llvm -verify %s
+// RUN: %clang_cc1 -fsycl -fsycl-is-device -triple spir64-unknown-unknown-sycldevice -verify -fsyntax-only %s
 // expected-no-diagnostics
-int foo();
+int foo();