[gegl] meson: Make "env" program optional

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 8e52e5ae4d6d2076433fe2f52c69959b4fa15b5c
Author: Xavier Claessens <xavier claessens collabora com>
Date:   Wed Apr 27 15:44:06 2022 -0400

    meson: Make "env" program optional
    
    This is a workaround while waiting for !123 to be merged when we'll
    depend on Meson 0.57.0.

 meson.build | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index f55a45e83..35c3ed702 100644
--- a/meson.build
+++ b/meson.build
@@ -231,7 +231,7 @@ add_project_arguments(cpp.get_supported_arguments(cflags_cpp), language: 'cpp')
 ################################################################################
 # Build Utilities
 
-env               = find_program('env')
+env               = find_program('env', required: false)
 
 asciidoc          = find_program('asciidoc',
                      required: false, native: true)
@@ -465,7 +465,7 @@ if get_option('docs') == 'auto'
   if meson.is_cross_build()
     build_docs = false
     message('configure with -Ddocs=true to cross-build docs')
-  elif not asciidoc.found()
+  elif not asciidoc.found() or not env.found()
     build_docs = false
   endif
 elif get_option('docs') == 'false'