meson: error out in script if gperf preprocessing failed

12 jobs for master in 19 minutes and 33 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #6678309
meson android arm64 fedora

00:01:50

passed #6678307
gst-macos-10.15
meson macos

00:05:05

passed #6678304
meson-mingw-w64-build

00:06:39

manual #6678308
docker windows 1809 allowed to fail manual
meson msys2
passed #6679059
meson-shared-build

00:06:03

passed #6678303
meson-static-build

00:06:53

passed #6678305
docker windows 1809
meson vs2017 amd64

00:01:30

passed #6678306
docker windows 1809
meson vs2017 x86

00:01:31

passed #6678301
mingw-build

00:07:11

passed #6678299
shared-build

00:08:24

passed #6678300
static-build

00:06:58

failed #6678302
meson-shared-build

00:06:25