CMP0141: Fix PCH REUSE_FROM when MSVC_DEBUG_INFORMATION_FORMAT is empty

Under the policy's NEW behavior, `[CMAKE_]MSVC_DEBUG_INFORMATION_FORMAT`
may be explicitly set to an empty string to tell CMake not to add any
flags for this abstraction.  In this case, fall back to checking the
language-wide flags as we do in the OLD behavior.

This revises commit 183b9a9eca (CMP0141: Fix PCH REUSE_FROM under policy
NEW behavior, 2022-10-31, v3.25.0-rc3~4^2).

Issue: #24106

Source/cmLocalGenerator.cxx

@@ -2677,8 +2677,10 @@ void cmLocalGenerator::AddPchDependencies(cmGeneratorTarget* target)
 
                 bool editAndContinueDebugInfo = false;
                 bool programDatabaseDebugInfo = false;
-                if (cm::optional<std::string> msvcDebugInformationFormat =
-                      this->GetMSVCDebugFormatName(config, target)) {
+                cm::optional<std::string> msvcDebugInformationFormat =
+                  this->GetMSVCDebugFormatName(config, target);
+                if (msvcDebugInformationFormat &&
+                    !msvcDebugInformationFormat->empty()) {
                   editAndContinueDebugInfo =
                     *msvcDebugInformationFormat == "EditAndContinue";
                   programDatabaseDebugInfo =

Tests/RunCMake/PrecompileHeaders/PchReuseFrom-CMP0141-NEW-empty.cmake

@@ -0,0 +1,4 @@
+cmake_policy(SET CMP0141 NEW)
+set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT "")
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -Zi")
+include(PchReuseFrom-common.cmake)

Tests/RunCMake/PrecompileHeaders/RunCMakeTest.cmake

@@ -17,6 +17,9 @@ run_test(SkipPrecompileHeaders)
 run_test(CXXnotC)
 run_test(PchReuseFrom-CMP0141-OLD)
 run_test(PchReuseFrom-CMP0141-NEW)
+if(CMAKE_C_COMPILER_ID STREQUAL "MSVC")
+  run_test(PchReuseFrom-CMP0141-NEW-empty)
+endif()
 run_test(PchReuseFromPrefixed)
 run_test(PchReuseFromSubdir)
 run_cmake(PchMultilanguage)