[OPENMP]Fix PR48759: "fatal error" when compile with preprocessed file.

[ABataev]

Summary

If the file in line directive does not exist on the system we need, to
use the original file to get its file id.

[mibintc]

Thanks @ABataev !

clang/lib/CodeGen/CGOpenMPRuntime.cpp

static void getTargetEntryUniqueInfo(ASTContext &C, SourceLocation Loc,
   // #pragma directives in macros)
 
   assert(Loc.isValid() && "Source location is expected to be always valid.");
 
   PresumedLoc PLoc = SM.getPresumedLoc(Loc);
   assert(PLoc.isValid() && "Source location is expected to be always valid.");
 
   llvm::sys::fs::UniqueID ID;
+  if (auto EC = llvm::sys::fs::getUniqueID(PLoc.getFilename(), ID)) {
+    PLoc = SM.getPresumedLoc(Loc, /*UseLineDirectives=*/false);
+    assert(PLoc.isValid() && "Source location is expected to be always valid.");
     if (auto EC = llvm::sys::fs::getUniqueID(PLoc.getFilename(), ID))
       SM.getDiagnostics().Report(diag::err_cannot_open_file)
           << PLoc.getFilename() << EC.message();
+  }
 
   DeviceID = ID.getDevice();
   FileID = ID.getFile();
   LineNum = PLoc.getLine();
 }
 
 Address CGOpenMPRuntime::getAddrOfDeclareTargetVar(const VarDecl *VD) {
   if (CGM.getLangOpts().OpenMPSimd)

clang/test/OpenMP/target_unknown_file.cpp

+// RUN: %clang_cc1 -verify -fopenmp -triple x86_64-apple-darwin10.6.0 -emit-llvm -o - %s 2>&1 | FileCheck %s
+// expected-no-diagnostics
+
+// CHECK-NOT: fatal error: cannot open file
+
+// CHECK: call void @__omp_offloading_{{.+}}()
+# 1 "unknown.xxxxxxxx"
+void a() {
+#pragma omp target
+  ;
+}
+
+// CHECK-NOT: fatal error: cannot open file