[Driver][SYCL] Allow for preprocessing to succeed with coding errors (#5784)

Typical behavior is to allow for preprocessing to succeed regardless of
the input file.  When building with -fsycl, this is not possible due to
the requirement to generate the integration ehader and footer before we do
the actual preprocessing step.

Adjust the compilation when preprocessing is requested to allow for
the device compilation to fail and continue to perform the preprocessing
steps.

Author: mdtoguchi

clang/lib/Driver/Compilation.cpp

@@ -236,6 +236,14 @@ int Compilation::ExecuteCommand(const Command &C,
     getDriver().Diag(diag::err_drv_command_failure) << Error;
   }
 
+  // When performing preprocessing, we need to be able to produce the
+  // preprocessed output even if the compilation is not valid.  If
+  // the device compilation fails for SYCL allow the failure to pass
+  // through so we can still generate the expected preprocessed files.
+  if (Res && C.getSource().isDeviceOffloading(Action::OFK_SYCL) &&
+      getArgs().hasArg(options::OPT_E))
+    return 0;
+
   if (Res)
     FailingCommand = &C;
 

clang/test/Driver/sycl-preproc-error.cpp

@@ -0,0 +1,9 @@
+/// Allow for preprocessing to 'succeed' even though there are coding issues
+/// in the source.  We always have an additional step to generate the
+/// integration header and footer, so if that fails we still want to produce
+/// preprocessing information in the subsequent passes.
+// RUN: %clang -fsycl -E -dM %s 2>&1 | FileCheck %s --check-prefix=PP_CHECK
+// PP_CHECK: SYCL_PP_CHECK
+
+void foo(;
+#define SYCL_PP_CHECK