clutter: Fix build with clang

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
Part-of: <!1668>
13 jobs for !1668 with clang in 21 minutes and 26 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #1082666
check-commit-log

00:00:46

passed #1082667
check-merge-request

00:00:14

 
  Prepare
passed #1082669
aarch64
build-fedora-container@aarch64

00:00:23

passed #1082668
build-fedora-container@x86_64

00:00:25

 
  Build
passed #1082671
aarch64
build-mutter@aarch64

00:06:24

passed #1082670
build-mutter@x86_64

00:02:07

passed #1082673
build-without-native-backend-and-wayland@x86_64

00:00:55

passed #1082672
build-without-opengl-and-glx@x86_64

00:01:48

 
  Test
passed #1082676
can-build-gnome-shell@x86_64

00:01:02

passed #1082675
aarch64
test-mutter@aarch64

00:06:43

passed #1082674
test-mutter@x86_64

00:03:35

 
  Coverage
passed #1082678
aarch64
test-mutter-coverage@aarch64

00:07:05

45.0%
passed #1082677
test-mutter-coverage@x86_64

00:03:29

45.0%