validate: silence g-ir-scanner warnings about GST_IS_VALIDATE_*

Which it complains about because we say our prefix is 'gst_validate'
so it should really be GST_VALIDATE_IS_* instead.

Hide the boilerplate defines from g-ir-scanner, it doesn't need
to process them.

Fixes #46

Part-of: <gstreamer/gst-devtools!214>
37 jobs for !214 with silence-g-ir-scanner-warnings in 43 minutes and 17 seconds (queued for 5 seconds)
detached
Status Job ID Name Coverage
  Build Docker
passed #3818845
alpine amd64 manifest builder docker

00:02:09

passed #3818843
android docker

00:00:32

passed #3818842
cerbero fedora amd64 docker

00:00:18

passed #3818840
fedora amd64 docker

00:00:19

passed #3818846
gst-indent amd64 docker

00:00:31

 
  Preparation
passed #3818850
gst indent

00:00:23

passed #3818848
manifest

00:01:30

 
  Build
passed #3818867
gstreamer
build cerbero cross-android universal

00:07:09

passed #3818875
gst-ios-13.2
build cerbero cross-ios universal

00:29:38

passed #3820933
gstreamer
build cerbero cross win32

00:03:23

passed #3818871
gstreamer
build cerbero cross win64

00:04:03

passed #3818865
gstreamer
build cerbero fedora x86_64

00:04:55

passed #3818873
gst-macos-10.15
build cerbero macos x86_64

00:08:16

passed #3818856
build clang fedora x86_64

00:09:28

manual #3818863
1809 windows docker allowed to fail manual
build msys2
passed #3818851
build nodebug fedora x86_64

00:02:54

passed #3818853
build static fedora x86_64

00:07:15

passed #3818855
build static nodebug fedora x86_64

00:07:44

passed #3818858
1809 windows docker
build vs2017 amd64

00:11:30

passed #3818861
1809 windows docker
build vs2017 x86

00:11:49

failed #3818869
gstreamer
build cerbero cross win32

00:02:34

 
  Test
passed #3818877
gstreamer
check fedora

00:05:14

passed #3818879
gstreamer
integration testsuites fedora 1/4

00:13:15

passed #3818881
gstreamer
integration testsuites fedora 2/4

00:14:49

passed #3818883
gstreamer
integration testsuites fedora 3/4

00:13:26

passed #3818886
gstreamer
integration testsuites fedora 4/4

00:14:38

passed #3818891
gstreamer
valgrind bad

00:07:53

passed #3818888
gstreamer
valgrind base

00:04:54

passed #3818887
gstreamer
valgrind core

00:05:28

passed #3818892
gstreamer
valgrind ges

00:07:52

passed #3820934
gstreamer
valgrind good

00:08:24

passed #3819612
gstreamer
valgrind ugly

00:02:45

failed #3818889
gstreamer
valgrind good

00:08:50

failed #3818890
gstreamer
valgrind ugly

00:02:10

 
  Integrate
passed #3818893
cross-android universal examples

00:11:13

passed #3818895
gst-ios-13.2
cross-ios universal examples

00:01:23

passed #3818894
documentation

00:14:33