[gcr] meson: allow building without gpg(2) installed

[Niels De Graef <nielsdg src gnome org>]

commit 5aa74c851419cf72da85ac5394f41ed86e6f8461
Author: Rasmus Thomsen <oss cogitri dev>
Date:   Wed Mar 11 11:49:08 2020 +0100

    meson: allow building without gpg(2) installed
    
    This avoids circular dependencies, such as gcr -> gpg2 -> pinentry -> gcr

 meson.build       | 7 +++++--
 meson_options.txt | 5 +++++
 2 files changed, 10 insertions(+), 2 deletions(-)
---
diff --git a/meson.build b/meson.build
index a26a0f92..02b4c3c6 100644
--- a/meson.build
+++ b/meson.build
@@ -41,7 +41,10 @@ gobject_dep = dependency('gobject-2.0', version: '>=' + min_glib_version)
 gio_dep = dependency('gio-2.0', version: '>=' + min_glib_version)
 gio_unix_dep = dependency('gio-unix-2.0',version: '>=' + min_glib_version)
 glib_deps = [ glib_dep, gmodule_dep, gthread_dep, gobject_dep, gio_dep, gio_unix_dep, ]
-gpg_bin = find_program('gpg2', 'gpg')
+gpg_path = get_option('gpg_path')
+if gpg_path == ''
+  gpg_path = find_program('gpg2', 'gpg').path()
+endif
 libgcrypt_dep = dependency('libgcrypt', version: '>= 1')
 p11kit_dep = dependency('p11-kit-1', version: '>= 0.19.0')
 p11_system_config_modules = p11kit_dep.get_pkgconfig_variable('p11_system_config_modules')
@@ -65,7 +68,7 @@ conf.set('HAVE_GETTEXT', true)
 conf.set('HAVE_LOCALE_H', cc.has_header('locale.h'))
 conf.set('HAVE_TIMEGM', cc.has_function('timegm'))
 conf.set('HAVE_MLOCK', cc.has_function('mlock'))
-conf.set_quoted('GPG_EXECUTABLE', gpg_bin.path())
+conf.set_quoted('GPG_EXECUTABLE', gpg_path)
 conf.set_quoted('LIBGCRYPT_VERSION', libgcrypt_dep.version())
 config_file = configure_file(
   output: 'config.h',
diff --git a/meson_options.txt b/meson_options.txt
index bbdc8e37..ae0f5243 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -13,3 +13,8 @@ option('gtk_doc',
   value: true,
   description: 'Build the reference documentation (requires gtk-doc)',
 )
+option('gpg_path',
+  type: 'string',
+  value: '',
+  description: 'Path to gpg, autodetected if not set',
+)