[LTO] Fix fat-lto output for -c -emit-llvm. (#79404)

Fix and add a test case for combining '-ffat-lto-objects -c -emit-llvm'
options and fix a spelling mistake in same test.

(cherry picked from commit f1b1611)

clang/lib/Driver/Driver.cpp

@@ -4764,9 +4764,9 @@ Action *Driver::ConstructPhaseAction(
   case phases::Backend: {
     if (isUsingLTO() && TargetDeviceOffloadKind == Action::OFK_None) {
       types::ID Output;
-      if (Args.hasArg(options::OPT_ffat_lto_objects))
-        Output = Args.hasArg(options::OPT_emit_llvm) ? types::TY_LTO_IR
-                                                     : types::TY_PP_Asm;
+      if (Args.hasArg(options::OPT_ffat_lto_objects) &&
+          !Args.hasArg(options::OPT_emit_llvm))
+        Output = types::TY_PP_Asm;
       else if (Args.hasArg(options::OPT_S))
         Output = types::TY_LTO_IR;
       else

clang/test/Driver/fat-lto-objects.c

@@ -23,11 +23,17 @@
 // CHECK-CC-S-EL-LTO-SAME: -emit-llvm
 // CHECK-CC-S-EL-LTO-SAME: -ffat-lto-objects
 
-/// When fat LTO is enabled wihtout -S we expect native object output and -ffat-lto-object to be passed to cc1.
+/// When fat LTO is enabled without -S we expect native object output and -ffat-lto-object to be passed to cc1.
 // RUN: %clang --target=x86_64-unknown-linux-gnu -flto -ffat-lto-objects -### %s -c 2>&1 | FileCheck %s -check-prefix=CHECK-CC-C-LTO
 // CHECK-CC-C-LTO: -cc1
-// CHECK-CC-C-LTO: -emit-obj
-// CHECK-CC-C-LTO: -ffat-lto-objects
+// CHECK-CC-C-LTO-SAME: -emit-obj
+// CHECK-CC-C-LTO-SAME: -ffat-lto-objects
+
+/// When fat LTO is enabled with -c and -emit-llvm we expect bitcode output and -ffat-lto-object to be passed to cc1.
+// RUN: %clang --target=x86_64-unknown-linux-gnu -flto -ffat-lto-objects -### %s -c -emit-llvm 2>&1 | FileCheck %s -check-prefix=CHECK-CC-C-EL-LTO
+// CHECK-CC-C-EL-LTO: -cc1
+// CHECK-CC-C-EL-LTO-SAME: -emit-llvm-bc
+// CHECK-CC-C-EL-LTO-SAME: -ffat-lto-objects
 
 /// Make sure we don't have a warning for -ffat-lto-objects being unused
 // RUN: %clang --target=x86_64-unknown-linux-gnu -ffat-lto-objects -fdriver-only -Werror -v %s -c 2>&1 | FileCheck %s -check-prefix=CHECK-CC-NOLTO