llvm: Set target-abi module flag.

LLVM is increasingly making use of this module flag when present.

Author: alexrp

src/codegen/llvm.zig

@@ -1110,14 +1110,24 @@ pub const Object = struct {
         }
 
         {
-            var module_flags = try std.ArrayList(Builder.Metadata).initCapacity(o.gpa, 7);
+            var module_flags = try std.ArrayList(Builder.Metadata).initCapacity(o.gpa, 8);
             defer module_flags.deinit();
 
             const behavior_error = try o.builder.metadataConstant(try o.builder.intConst(.i32, 1));
             const behavior_warning = try o.builder.metadataConstant(try o.builder.intConst(.i32, 2));
             const behavior_max = try o.builder.metadataConstant(try o.builder.intConst(.i32, 7));
             const behavior_min = try o.builder.metadataConstant(try o.builder.intConst(.i32, 8));
 
+            if (target_util.llvmMachineAbi(comp.root_mod.resolved_target.result)) |abi| {
+                module_flags.appendAssumeCapacity(try o.builder.metadataModuleFlag(
+                    behavior_error,
+                    try o.builder.metadataString("target-abi"),
+                    try o.builder.metadataConstant(
+                        try o.builder.stringConst(try o.builder.string(abi)),
+                    ),
+                ));
+            }
+
             const pic_level = target_util.picLevel(comp.root_mod.resolved_target.result);
             if (comp.root_mod.pic) {
                 module_flags.appendAssumeCapacity(try o.builder.metadataModuleFlag(