[gtk-vnc] meson: only run syntax-check if runnin from git

[Daniel P. Berrange <dberrange src gnome org>]

commit 99db41b631d1ffe5b9ddbdf728813abc113e45d2
Author: Daniel P. Berrangé <dan berrange com>
Date:   Tue Apr 13 14:42:39 2021 +0100

    meson: only run syntax-check if runnin from git
    
    The syntax-check rules use git to get a list of files to check.
    
    Signed-off-by: Daniel P. Berrangé <berrange redhat com>

 meson.build | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index e2b31d1..16a5e21 100644
--- a/meson.build
+++ b/meson.build
@@ -24,14 +24,18 @@ conf_data.set('version_micro', version_micro)
 # ninja dist helper
 meson.add_dist_script('build-aux/dist.sh', meson.source_root(), meson.build_root())
 
-test(
+git = run_command('test', '-d', '.git').returncode() == 0
+
+if git
+  test(
     'syntax-check',
     find_program('@0@/build-aux/syntax-check'.format(meson.source_root())),
     suite: 'style',
     env: [
         'MESON_SOURCE_ROOT=@0@'.format(meson.source_root()),
     ],
-)
+  )
+endif
 
 pod2man = find_program('pod2man')