meson.build: enable CPP include check only in case CPP compiler is available

Drop hard meson C++/CPP dependency, only needed for the build-time
header inclusion test, build the test only in case C++/CPP compiler
is available.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
44 jobs for master in 29 minutes and 3 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Bootstrapping
manual bootstrap #80998
allowed to fail manual
 
  Container Check
passed arch:rolling@container-check #81003

00:00:21

passed arch:rolling@container-clean #81010

00:00:47

passed bootstrap@container-clean #81005

00:00:38

passed fedora:28@container-check #80999

00:00:31

passed fedora:28@container-clean #81006

00:00:45

passed fedora:29@container-check #81000

00:00:15

passed fedora:29@container-clean #81007

00:00:28

passed freebsd:11.2@container-check #81004

00:00:27

passed freebsd:11.2@container-clean #81011

00:00:48

passed ubuntu:18.04@container-check #81002

00:00:29

passed ubuntu:18.04@container-clean #81009

00:00:28

passed ubuntu:18.10@container-check #81001

00:00:15

passed ubuntu:18.10@container-clean #81008

00:00:47

 
  Container Prep
passed arch:rolling@container-prep #81016

00:00:20

manual arch:rolling@force-container-prep #81022
allowed to fail manual
passed fedora:28@container-prep #81012

00:00:17

manual fedora:28@force-container-prep #81018
allowed to fail manual
passed fedora:29@container-prep #81013

00:00:17

manual fedora:29@force-container-prep #81019
allowed to fail manual
passed freebsd:11.2@container-prep #81017

00:00:20

manual freebsd:11.2@force-container-prep #81023
allowed to fail manual
passed ubuntu:18.04@container-prep #81015

00:00:21

manual ubuntu:18.04@force-container-prep #81021
allowed to fail manual
passed ubuntu:18.10@container-prep #81014

00:00:17

manual ubuntu:18.10@force-container-prep #81020
allowed to fail manual
 
  Build
passed arch:rolling@default-build #81039

00:00:48

passed fedora:28@default-build #81024

00:00:45

passed fedora:29@build-no-debuggui #81032

00:00:36

passed fedora:29@build-no-debuggui-nodeps #81033

00:00:45

passed fedora:29@build-no-docs #81030

00:00:40

passed fedora:29@build-no-docs-nodeps #81031

00:00:39

passed fedora:29@build-no-libwacom #81028

00:00:47

passed fedora:29@build-no-libwacom-nodeps #81029

00:00:48

passed fedora:29@build-no-tests #81034

00:00:39

passed fedora:29@build-no-tests-nodeps #81035

00:00:33

passed fedora:29@default-build #81025

00:00:34

passed fedora:29@default-build-release #81026

00:00:38

passed fedora:29@scan-build #81027

00:27:30

passed fedora:29@valgrind #81036

00:00:51

passed freebsd:11.2@default-build #81040

00:00:44

passed ubuntu:18.04@default-build #81038

00:00:54

passed ubuntu:18.10@default-build #81037

00:00:45

 
  Deploy
passed wayland-web #81041

00:00:19