ninja: Always treat PCHs as an implicit dependency

In addition to MSVC, which was worked around previously, GCC also does
not list includes from the PCH in the depfile by default, unless
-fpch-deps is given. I think it's best to stay safe and not rely on any
particular behavior from the compiler here.

mesonbuild/backend/ninjabackend.py

@@ -2219,14 +2219,7 @@ rule FORTRAN_DEP_HACK%s
             elif not self.has_dir_part(d):
                 d = os.path.join(self.get_target_private_dir(target), d)
             element.add_orderdep(d)
-        if compiler.id == 'msvc':
-            # MSVC does not show includes coming from the PCH with '/showIncludes',
-            # thus we must add an implicit dependency to the generated PCH.
-            element.add_dep(pch_dep)
-        else:
-            # All other compilers properly handle includes through the PCH, so only an
-            # orderdep is needed to make the initial build without depfile work.
-            element.add_orderdep(pch_dep)
+        element.add_dep(pch_dep)
         # Convert from GCC-style link argument naming to the naming used by the
         # current compiler.
         commands = commands.to_native()