ninjabackend: Treat GNOME gir/typelib as libraries

When classifying generated sources, we were treating gir/typelib files
generated by gobject-introspection as headers. This is bad because it
serializes the build by adding order-only dependencies to every target
even though sources will never actually use them for anything.

Treat them as libraries, which is somewhat more accurate.

mesonbuild/backend/ninjabackend.py

@@ -570,7 +570,7 @@ int dummy;
                     generated_source_files.append(raw_src)
             elif self.environment.is_object(rel_src):
                 obj_list.append(rel_src)
-            elif self.environment.is_library(rel_src):
+            elif self.environment.is_library(rel_src) or modules.is_module_library(rel_src):
                 pass
             else:
                 # Assume anything not specifically a source file is a header. This is because

mesonbuild/modules/__init__.py

@@ -57,6 +57,17 @@ def get_include_args(include_dirs, prefix='-I'):
 
     return dirs_str
 
+def is_module_library(fname):
+    '''
+    Check if the file is a library-like file generated by a module-specific
+    target, such as GirTarget or TypelibTarget
+    '''
+    if hasattr(fname, 'fname'):
+        fname = fname.fname
+    suffix = fname.split('.')[-1]
+    return suffix in ('gir', 'typelib')
+
+
 class ModuleReturnValue:
     def __init__(self, return_value, new_objects):
         self.return_value = return_value