[lld-macho] Find objects in library search path (#78628)

Find object files in library search path just like Apple's linker, this
makes building with some older MacOS SDKs easier since clang runs with
`-lcrt1.10.6.o`

Author: Un1q32

lld/MachO/Driver.cpp

@@ -90,6 +90,10 @@ static std::optional<StringRef> findLibrary(StringRef name) {
     return entry->second;
 
   auto doFind = [&] {
+    // Special case for Csu support files required for Mac OS X 10.7 and older
+    // (crt1.o)
+    if (name.ends_with(".o"))
+      return findPathCombination(name, config->librarySearchPaths, {""});
     if (config->searchDylibsFirst) {
       if (std::optional<StringRef> path =
               findPathCombination("lib" + name, config->librarySearchPaths,

lld/test/MachO/link-csu-object.s

@@ -0,0 +1,14 @@
+# REQUIRES: x86
+# RUN: mkdir -p %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %p/Inputs/libhello.s -o %t/hello.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/main.o
+# RUN: %lld -L %t %t/main.o %t/hello.o -o %t/a.out
+# RUN: llvm-nm %t/a.out | FileCheck %s
+
+# CHECK: _main
+# CHECK: _print_hello
+
+.globl _main
+_main:
+    call _print_hello
+    ret