Use .init_array rather than .ctors

LLVM TargetMachines default to using the (now-legacy) .ctors
representation of init functions. Mixing .ctors and .init_array
representations can cause issues when linking with lld.

This happens in practice for:

* Our profiling runtime which is currently implicitly built with
  .init_array since it is built by clang, which sets this field.
* External C/C++ code that may be linked into the same process.

To support legacy systems which may use .ctors, targets may now specify
that they use .ctors via the use_ctors attribute which defaults to
false.

For debugging and manual control, -Z use-ctors-section=yes/no will allow
manual override.

Fixes: #71233

src/rustllvm/PassWrapper.cpp

@@ -445,7 +445,8 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     bool Singlethread,
     bool AsmComments,
     bool EmitStackSizeSection,
-    bool RelaxELFRelocations) {
+    bool RelaxELFRelocations,
+    bool UseInitArray) {
 
   auto OptLevel = fromRust(RustOptLevel);
   auto RM = fromRust(RustReloc);
@@ -471,6 +472,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   Options.MCOptions.PreserveAsmComments = AsmComments;
   Options.MCOptions.ABIName = ABIStr;
   Options.RelaxELFRelocations = RelaxELFRelocations;
+  Options.UseInitArray = UseInitArray;
 
   if (TrapUnreachable) {
     // Tell LLVM to codegen `unreachable` into an explicit trap instruction.