Fix: don't set external linkage when @[NoInline] is specified (#15424)

Unlike `alwaysinline` that is treated by LLVM as a simple hint, the
`noinline` function attribute is enough to tell LLVM to always generate
the symbol and never inline the calls (even with aggressive
optimizations).

We don't need to set the linkage to external.

Author: ysbaddaden

src/compiler/crystal/codegen/fun.cr

@@ -337,7 +337,7 @@ class Crystal::CodeGenVisitor
       end
     end
 
-    if @single_module && !target_def.no_inline? && !target_def.is_a?(External)
+    if @single_module && !target_def.is_a?(External)
       context.fun.linkage = LLVM::Linkage::Internal
     end
 
@@ -448,11 +448,7 @@ class Crystal::CodeGenVisitor
     context.fun.add_attribute LLVM::Attribute::ReturnsTwice if target_def.returns_twice?
     context.fun.add_attribute LLVM::Attribute::Naked if target_def.naked?
     context.fun.add_attribute LLVM::Attribute::NoReturn if target_def.no_returns?
-
-    if target_def.no_inline?
-      context.fun.add_attribute LLVM::Attribute::NoInline
-      context.fun.linkage = LLVM::Linkage::External
-    end
+    context.fun.add_attribute LLVM::Attribute::NoInline if target_def.no_inline?
   end
 
   def setup_closure_vars(def_vars, closure_vars, context, closure_type, closure_ptr)