build: add a few annotations

I was debugging this code, these were trivial, so I added them.

mesonbuild/build.py

@@ -304,22 +304,22 @@ class Build:
     def get_install_subdirs(self):
         return self.install_dirs
 
-    def get_global_args(self, compiler, for_machine):
+    def get_global_args(self, compiler: 'Compiler', for_machine: 'MachineChoice') -> T.List[str]:
         d = self.global_args[for_machine]
         return d.get(compiler.get_language(), [])
 
-    def get_project_args(self, compiler, project, for_machine):
+    def get_project_args(self, compiler: 'Compiler', project: str, for_machine: 'MachineChoice') -> T.List[str]:
         d = self.projects_args[for_machine]
         args = d.get(project)
         if not args:
             return []
         return args.get(compiler.get_language(), [])
 
-    def get_global_link_args(self, compiler, for_machine):
+    def get_global_link_args(self, compiler: 'Compiler', for_machine: 'MachineChoice') -> T.List[str]:
         d = self.global_link_args[for_machine]
         return d.get(compiler.get_language(), [])
 
-    def get_project_link_args(self, compiler, project, for_machine):
+    def get_project_link_args(self, compiler: 'Compiler', project: str, for_machine: 'MachineChoice') -> T.List[str]:
         d = self.projects_link_args[for_machine]
 
         link_args = d.get(project)