gnome: Pass ExternalProgram objects to CustomTarget

There is no need to do obj.get_command() and in fact it's wrong
because the VS backends need to resolve each object to absolute paths
and get_command() does not do that.

This should fix invocation of GNOME module helpers with the VS backends

For the record, absolute paths for programs are needed because the
same PATH environment won't necessarily be available to Visual Studio
when it builds the generated solution.

Related to https://github.com/mesonbuild/meson/issues/1419

mesonbuild/modules/gnome.py

@@ -379,7 +379,7 @@ class GnomeModule(ExtensionModule):
         depends = [girtarget]
         gir_inc_dirs = []
 
-        scan_command = giscanner.get_command() + ['@INPUT@']
+        scan_command = [giscanner, '@INPUT@']
         scan_command += pkgargs
         scan_command += ['--no-libtool', '--namespace=' + ns, '--nsversion=' + nsversion, '--warn-all',
                          '--output', '@OUTPUT@']
@@ -535,7 +535,7 @@ class GnomeModule(ExtensionModule):
         scan_target = GirTarget(girfile, state.subdir, scankwargs)
 
         typelib_output = '%s-%s.typelib' % (ns, nsversion)
-        typelib_cmd = gicompiler.get_command() + [scan_target, '--output', '@OUTPUT@']
+        typelib_cmd = [gicompiler, scan_target, '--output', '@OUTPUT@']
         typelib_cmd += get_include_args(state.environment, gir_inc_dirs,
                                         prefix='--includedir=')
         for incdir in typelib_includes:
@@ -559,7 +559,7 @@ class GnomeModule(ExtensionModule):
         srcdir = os.path.join(state.build_to_src, state.subdir)
         outdir = state.subdir
 
-        cmd = find_program('glib-compile-schemas', 'gsettings-compile').get_command()
+        cmd = [find_program('glib-compile-schemas', 'gsettings-compile')]
         cmd += ['--targetdir', outdir, srcdir]
         kwargs['command'] = cmd
         kwargs['input'] = []
@@ -753,7 +753,7 @@ class GnomeModule(ExtensionModule):
         namebase = args[0]
         xml_file = args[1]
         target_name = namebase + '-gdbus'
-        cmd = find_program('gdbus-codegen', target_name).get_command()
+        cmd = [find_program('gdbus-codegen', target_name)]
         if 'interface_prefix' in kwargs:
             cmd += ['--interface-prefix', kwargs.pop('interface_prefix')]
         if 'namespace' in kwargs:
@@ -811,7 +811,7 @@ class GnomeModule(ExtensionModule):
             elif arg not in known_custom_target_kwargs:
                 raise MesonException(
                     'Mkenums does not take a %s keyword argument.' % (arg, ))
-        cmd = find_program('glib-mkenums', 'mkenums').get_command() + cmd
+        cmd = [find_program('glib-mkenums', 'mkenums')] + cmd
         custom_kwargs = {}
         for arg in known_custom_target_kwargs:
             if arg in kwargs:
@@ -894,7 +894,7 @@ class GnomeModule(ExtensionModule):
             raise MesonException(
                 'Sources keyword argument must be a string or array.')
 
-        cmd = find_program('glib-genmarshal', output + '_genmarshal').get_command()
+        cmd = [find_program('glib-genmarshal', output + '_genmarshal')]
         known_kwargs = ['internal', 'nostdinc', 'skip_source', 'stdinc',
                         'valist_marshallers']
         known_custom_target_kwargs = ['build_always', 'depends',
@@ -1023,7 +1023,7 @@ class GnomeModule(ExtensionModule):
         build_dir = os.path.join(state.environment.get_build_dir(), state.subdir)
         source_dir = os.path.join(state.environment.get_source_dir(), state.subdir)
         pkg_cmd, vapi_depends, vapi_packages, vapi_includes = self._extract_vapi_packages(state, kwargs)
-        cmd = find_program('vapigen', 'Vaapi').get_command()
+        cmd = [find_program('vapigen', 'Vaapi')]
         cmd += ['--quiet', '--library=' + library, '--directory=' + build_dir]
         cmd += self._vapi_args_to_command('--vapidir=', 'vapi_dirs', kwargs)
         cmd += self._vapi_args_to_command('--metadatadir=', 'metadata_dirs', kwargs)