Dispose LLVM context after TargetMachine

The TargetMachine may be referencing data in the context. In
particular, at least the GlobalISel instruction selector stored
in the TM may reference a TrackedMDNode DebugLoc that destruction
of the TargetMachine will try to untrack.

compiler/rustc_codegen_llvm/src/lib.rs

@@ -352,8 +352,8 @@ impl ModuleLlvm {
 impl Drop for ModuleLlvm {
     fn drop(&mut self) {
         unsafe {
-            llvm::LLVMContextDispose(&mut *(self.llcx as *mut _));
             llvm::LLVMRustDisposeTargetMachine(&mut *(self.tm as *mut _));
+            llvm::LLVMContextDispose(&mut *(self.llcx as *mut _));
         }
     }
 }