[Driver][SYCL] Put implied src header search before user settings (#4435)

When compiling the src+footer file, perform the header search in the
src directory before any user specified directories.

Author: mdtoguchi

clang/lib/Driver/ToolChains/Clang.cpp

@@ -1432,14 +1432,11 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     A->render(Args, CmdArgs);
   }
 
-  Args.AddAllArgs(CmdArgs,
-                  {options::OPT_D, options::OPT_U, options::OPT_I_Group,
-                   options::OPT_F, options::OPT_index_header_map});
-
   // The file being compiled that contains the integration footer is not being
   // compiled in the directory of the original source.  Add that directory
-  // as an -internal-isystem option so we can properly find potential headers
-  // there.
+  // as an -I option so we can properly find potential headers there.  The
+  // original source search directory should also be placed before any user
+  // search directories.
   if (ContainsAppendFooterAction(&JA)) {
     SmallString<128> SourcePath(Inputs[0].getBaseInput());
     llvm::sys::path::remove_filename(SourcePath);
@@ -1453,6 +1450,10 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
     }
   }
 
+  Args.AddAllArgs(CmdArgs,
+                  {options::OPT_D, options::OPT_U, options::OPT_I_Group,
+                   options::OPT_F, options::OPT_index_header_map});
+
   // Add -Wp, and -Xpreprocessor if using the preprocessor.
 
   // FIXME: There is a very unfortunate problem here, some troubled

clang/test/Driver/sycl-int-footer.cpp

@@ -3,7 +3,7 @@
 // RUN:   | FileCheck -check-prefix FOOTER %s -DSRCDIR=%/S -DCMDDIR=cmdline/dir
 // FOOTER: clang{{.*}} "-fsycl-is-device"{{.*}} "-fsycl-int-header=[[INTHEADER:.+\.h]]" "-fsycl-int-footer=[[INTFOOTER:.+\h]]" "-sycl-std={{.*}}"{{.*}} "-include" "dummy.h"
 // FOOTER: append-file{{.*}} "[[INPUTFILE:.+\.cpp]]" "--append=[[INTFOOTER]]" "--orig-filename=[[INPUTFILE]]" "--output=[[APPENDEDSRC:.+\.cpp]]"
-// FOOTER: clang{{.*}} "-include" "[[INTHEADER]]"{{.*}} "-fsycl-is-host"{{.*}} "-include" "dummy.h"{{.*}} "-I" "cmdline/dir" "-I" "[[SRCDIR]]"
+// FOOTER: clang{{.*}} "-include" "[[INTHEADER]]"{{.*}} "-fsycl-is-host"{{.*}} "-include" "dummy.h"{{.*}} "-I" "[[SRCDIR]]" "-I" "cmdline/dir"
 // FOOTER-NOT: "-include" "[[INTHEADER]]"
 
 /// Preprocessed file creation with integration footer