Support per-language library link flags

This changes the behaviour of the generators to use a per-language
library search path flag.  This is needed for multi-language projects
with different compilers (e.g. cl + gfortran).  Since the adjusted
variable has been part of the user settings, we control this based on a
policy.

Fixes: #19307

Modules/CMakeSwiftInformation.cmake

@@ -23,6 +23,8 @@ set(CMAKE_Swift_COMPILE_OPTIONS_TARGET "-target ")
 set(CMAKE_Swift_COMPILER_ARG1 -frontend)
 set(CMAKE_Swift_DEFINE_FLAG -D)
 set(CMAKE_Swift_FRAMEWORK_SEARCH_FLAG "-F ")
+set(CMAKE_Swift_LIBRARY_PATH_FLAG "-L ")
+set(CMAKE_Swift_LIBRARY_PATH_TERMINATOR "")
 set(CMAKE_Swift_LINKER_WRAPPER_FLAG "-Xlinker" " ")
 set(CMAKE_Swift_RESPONSE_FILE_LINK_FLAG @)
 

Source/cmLocalGenerator.cxx

@@ -1444,10 +1444,23 @@ void cmLocalGenerator::OutputLinkLibraries(
 
   std::string linkLanguage = cli.GetLinkLanguage();
 
-  const std::string& libPathFlag =
-    this->Makefile->GetRequiredDefinition("CMAKE_LIBRARY_PATH_FLAG");
-  const std::string& libPathTerminator =
-    this->Makefile->GetSafeDefinition("CMAKE_LIBRARY_PATH_TERMINATOR");
+  std::string libPathFlag;
+  if (const char* value = this->Makefile->GetDefinition(
+        "CMAKE_" + cli.GetLinkLanguage() + "_LIBRARY_PATH_FLAG")) {
+    libPathFlag = value;
+  } else {
+    libPathFlag =
+      this->Makefile->GetRequiredDefinition("CMAKE_LIBRARY_PATH_FLAG");
+  }
+
+  std::string libPathTerminator;
+  if (const char* value = this->Makefile->GetDefinition(
+        "CMAKE_" + cli.GetLinkLanguage() + "_LIBRARY_PATH_TERMINATOR")) {
+    libPathTerminator = value;
+  } else {
+    libPathTerminator =
+      this->Makefile->GetRequiredDefinition("CMAKE_LIBRARY_PATH_TERMINATOR");
+  }
 
   // Add standard libraries for this language.
   std::string standardLibsVar = "CMAKE_";