[driver] Allow ld as a driver alias to lld (#90515)

This adds a "hidden" alias kind that allows using LLD when symlinked as
`ld`; however, it does not install `ld` as a symlink. This is to allow
either using a mixed toolchain with both LLD and GNU ld, or a pure LLD
toolchain where LLD has been installed (or symlinked) to `ld` for
compatibility w/ older tools that expect `ld`.

lld/tools/lld/CMakeLists.txt

@@ -42,3 +42,7 @@ endif()
 foreach(link ${LLD_SYMLINKS_TO_CREATE})
   add_lld_symlink(${link} lld)
 endforeach()
+
+if(LLVM_TOOL_LLVM_DRIVER_BUILD)
+  set_property(GLOBAL APPEND PROPERTY LLVM_DRIVER_HIDDEN_TOOL_ALIASES_lld ld)
+endif()

llvm/test/tools/llvm-driver/passthrough-lld.test

@@ -1,6 +1,8 @@
 # REQUIRES: llvm-driver, lld
 
 # RUN: %llvm ld.lld --help | FileCheck %s
+# RUN: %llvm ld --help | FileCheck %s
 # RUN: %llvm lld -flavor ld.lld --help | FileCheck %s
+# RUN: %llvm ld -flavor ld.lld --help | FileCheck %s
 
 # CHECK: supported targets: elf

llvm/tools/llvm-driver/CMakeLists.txt

@@ -13,6 +13,11 @@ foreach(tool ${LLVM_DRIVER_TOOLS})
     string(REPLACE "llvm-" "" alias ${alias})
     set(def_decl "${def_decl}LLVM_DRIVER_TOOL(\"${alias}\", ${tool_entry})\n")
   endforeach()
+  get_property(hidden_tool_aliases GLOBAL PROPERTY LLVM_DRIVER_HIDDEN_TOOL_ALIASES_${tool})
+  foreach(alias ${hidden_tool_aliases})
+    string(REPLACE "llvm-" "" alias ${alias})
+    set(def_decl "${def_decl}LLVM_DRIVER_TOOL(\"${alias}\", ${tool_entry})\n")
+  endforeach()
 endforeach()
 
 file(WRITE

utils/bazel/llvm-project-overlay/llvm/driver.bzl

@@ -37,7 +37,7 @@ _TOOLS = {
 # aliases for a given tool.
 _EXTRA_ALIASES = {
     "clang": ["clang++", "clang-cl", "clang-cpp"],
-    "lld": ["lld-link", "ld.lld", "ld64.lld", "wasm-ld"],
+    "lld": ["ld", "lld-link", "ld.lld", "ld64.lld", "wasm-ld"],
     "llvm-ar": ["ranlib", "lib", "dlltool"],
     "llvm-objcopy": ["bitcode-strip", "install-name-tool", "strip"],
     "llvm-objdump": ["otool"],