[Driver][SYCL] Disable the warning when fsycl-host-compiler is used (#5124)

The warning is emitted because we aren't doing any host compilation at that point. But the warning can be misleading to the users, they may think there is something inappropriate with usage of -fsycl-host-compiler. So instead of asking user not to use the option we are just ignoring the warning.

Author: hchilama

clang/include/clang/Driver/Options.td

@@ -2699,7 +2699,7 @@ def fsycl_libspirv_path_EQ : Joined<["-"], "fsycl-libspirv-path=">,
   Flags<[CC1Option, CoreOption]>, HelpText<"Path to libspirv library">;
 def fno_sycl_libspirv : Flag<["-"], "fno-sycl-libspirv">, Flags<[CoreOption]>, HelpText<"Disable check for libspirv">;
 def fsycl_host_compiler_EQ : Joined<["-"], "fsycl-host-compiler=">,
-  Flags<[CoreOption]>, HelpText<"Specify C++ compiler binary to perform host "
+  Flags<[CoreOption, NoArgumentUnused]>, HelpText<"Specify C++ compiler binary to perform host "
   "compilation with during SYCL offload compiles.">;
 def fsycl_host_compiler_options_EQ : Joined<["-"], "fsycl-host-compiler-options=">,
   Flags<[CoreOption]>, HelpText<"When performing the host compilation with "

clang/test/Driver/sycl-host-compiler.cpp

@@ -62,3 +62,9 @@
 // RUN: %clangxx -fsycl -fsycl-host-compiler= -c -### %s 2>&1 \
 // RUN:  | FileCheck -check-prefix=HOST_COMPILER_NOARG %s
 // HOST_COMPILER_NOARG: missing argument to '-fsycl-host-compiler='
+
+/// Warning should not be emitted when using -fsycl-host-compiler when linking
+// RUN: touch %t.o
+// RUN: %clangxx -fsycl -fsycl-host-compiler=g++ %t.o -### 2>&1 \
+// RUN:  | FileCheck -check-prefix=WARNING_HOST_COMPILER %s
+// WARNING_HOST_COMPILER-NOT: warning: argument unused during compilation: '-fsycl-host-compiler=g++' [-Wunused-command-line-argument]