Add options to specify linker tool

Offer the capability, through variable `CMAKE_LINKER_TYPE`, as well as
the target property `LINKER_TYPE` to specify which linker must be used.

The implementation of this capability is specified by variables specific
to the language and linker type: `CMAKE_<LANG>_USING_LINKER_<TYPE>`.
Some definitions are provided as part of `CMake`.

For example, to select the `LLVM` linker rather than the standard one,
the type `LLD` should be specified through the variable `CMAKE_LINKER_TYPE`.
And, on `Apple`, `Linux` and some environments on `Windows`, the variable
`CMAKE_<LANG>_USING_LINKER_LLD` has value `-fuse-ld=lld`. And for `Windows`
environments  based on `MSVC`, where the linker is used directly, the tool
`lld-link.exe` will be used rather than `link.exe`.

Fixes: #19174, #24254, #24990

1 files changed, 14 insertions, 11 deletions

diff --git a/Source/cmRulePlaceholderExpander.cxx b/Source/cmRulePlaceholderExpander.cxx
index 638bb42..a8c81d0 100644
--- a/Source/cmRulePlaceholderExpander.cxx
+++ b/Source/cmRulePlaceholderExpander.cxx
@@ -27,6 +27,19 @@ std::string cmRulePlaceholderExpander::ExpandVariable(
       return this->ReplaceValues->LinkFlags;
     }
   }
+  if (this->ReplaceValues->Linker) {
+    if (variable == "CMAKE_LINKER") {
+      auto result = this->OutputConverter->ConvertToOutputForExisting(
+        this->ReplaceValues->Linker);
+      if (this->ReplaceValues->Launcher) {
+        // Add launcher as part of expansion so that it always appears
+        // immediately before the command itself, regardless of whether the
+        // overall rule template contains other content at the front.
+        result = cmStrCat(this->ReplaceValues->Launcher, " ", result);
+      }
+      return result;
+    }
+  }
   if (this->ReplaceValues->Manifests) {
     if (variable == "MANIFESTS") {
       return this->ReplaceValues->Manifests;
@@ -325,17 +338,7 @@ std::string cmRulePlaceholderExpander::ExpandVariable(
   auto mapIt = this->VariableMappings.find(variable);
   if (mapIt != this->VariableMappings.end()) {
     if (variable.find("_FLAG") == std::string::npos) {
-      std::string ret =
-        this->OutputConverter->ConvertToOutputForExisting(mapIt->second);
-
-      if (this->ReplaceValues->Launcher && variable == "CMAKE_LINKER") {
-        // Add launcher as part of expansion so that it always appears
-        // immediately before the command itself, regardless of whether the
-        // overall rule template contains other content at the front.
-        ret = cmStrCat(this->ReplaceValues->Launcher, " ", ret);
-      }
-
-      return ret;
+      return this->OutputConverter->ConvertToOutputForExisting(mapIt->second);
     }
     return mapIt->second;
   }