[LLD] [COFF] Prefer paths specified with -libpath: over toolchain paths (#78039)

The main reason for adding the toolchain paths early was to prefer
libraries from the toolchain over ones from MSVC (primarily for
compiler-rt builtins). But if the user specifies a directory explicitly
with the -libpath: option, that should be preferred over the built-in
default paths.

This fixes an issue raised at
https://discourse.llvm.org/t/lld-prefers-system-llvm-libraries-to-user-provided-ones-on-windows/76148.

Author: mstorsjo

lld/COFF/Driver.cpp

@@ -1548,15 +1548,13 @@ void LinkerDriver::linkerMain(ArrayRef<const char *> argsArr) {
   {
     llvm::TimeTraceScope timeScope2("Search paths");
     searchPaths.emplace_back("");
+    for (auto *arg : args.filtered(OPT_libpath))
+      searchPaths.push_back(arg->getValue());
     if (!config->mingw) {
       // Prefer the Clang provided builtins over the ones bundled with MSVC.
       // In MinGW mode, the compiler driver passes the necessary libpath
       // options explicitly.
       addClangLibSearchPaths(argsArr[0]);
-    }
-    for (auto *arg : args.filtered(OPT_libpath))
-      searchPaths.push_back(arg->getValue());
-    if (!config->mingw) {
       // Don't automatically deduce the lib path from the environment or MSVC
       // installations when operating in mingw mode. (This also makes LLD ignore
       // winsysroot and vctoolsdir arguments.)

lld/test/COFF/print-search-paths.s

@@ -1,10 +1,11 @@
 # REQUIRES: x86
 # RUN: llvm-mc -triple x86_64-windows-msvc %s -filetype=obj -o %t.obj
-# RUN: lld-link -safeseh:no /dll /noentry /winsysroot:%t.dir/sysroot /vctoolsversion:1.1.1.1 /winsdkversion:10.0.1 %t.obj -print-search-paths | FileCheck -DSYSROOT=%t.dir %s
+# RUN: lld-link -safeseh:no /dll /noentry /winsysroot:%t.dir/sysroot /vctoolsversion:1.1.1.1 /winsdkversion:10.0.1 /libpath:custom-dir %t.obj -print-search-paths | FileCheck -DSYSROOT=%t.dir %s
 # RUN: llvm-mc -triple i686-windows-msvc %s -filetype=obj -o %t_32.obj
 # RUN: lld-link -safeseh:no /dll /noentry /winsysroot:%t.dir/sysroot /vctoolsversion:1.1.1.1 /winsdkversion:10.0.1 %t_32.obj -print-search-paths | FileCheck -DSYSROOT=%t.dir -check-prefix=X86 %s
 # CHECK: Library search paths:
 # CHECK-NEXT:   (cwd)
+# CHECK-NEXT:   custom-dir
 # CHECK-NEXT:   [[CPATH:.*]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib{{[/\\]}}windows
 # CHECK-NEXT:   [[CPATH]]lib{{[/\\]}}clang{{[/\\]}}{{[0-9]+}}{{[/\\]}}lib
 # CHECK-NEXT:   [[CPATH]]lib