[PATCH libgpiod] build: do not require a C++ compiler if it is not needed

Languages specified in the meson project() function are considered hard
dependencies. When trying to build libgpiod in an environment lacking a
C++ compiler, the build fails with an obscure error message ("ERROR:
Unable to get gcc pre-processor defines").

As the C++ compiler is only needed for building the C++ bindings, do not
require it unless the option bindings-cxx is enabled.

Signed-off-by: Edgar Bonet <[email protected]>
---
Note that this issue has caused a few failures on the Buildroot
autobuilders, e.g.:
https://autobuild.buildroot.org/results/d1c19ffa0c599bd2ba9be965a98fc8f778d6e366
https://autobuild.buildroot.org/results/c6b3c9311d628bdb4ea103431767493fab9a3668
https://autobuild.buildroot.org/results/8e799050c5779c680ff5e5136571f57d29239f2f
https://autobuild.buildroot.org/results/d6d8833acfe00559579defbbf3ca34c0edbe7869
---
 meson.build | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/meson.build b/meson.build
index 7a6306d..a8a5b0b 100644
--- a/meson.build
+++ b/meson.build
@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-or-later
 # SPDX-FileCopyrightText: 2026 Qualcomm Technologies, Inc. and/or its subsidiaries
 
-project('libgpiod', ['c', 'cpp'],
+project('libgpiod', 'c',
   version: '2.4',
   license: 'LGPL-2.1-or-later',
   default_options: [
@@ -56,6 +56,10 @@ opt_dbus                = get_option('dbus')
 opt_introspection       = get_option('introspection')
 opt_systemd             = get_option('systemd')
 
+if opt_bindings_cxx.allowed()
+  add_languages('cpp')
+endif
+
 if get_option('profiling')
   profiling_c_args    = ['-fprofile-arcs', '-ftest-coverage']
   profiling_link_args = ['-lgcov']

base-commit: 7d7b07738885d051a28bdfb5025c8eb73cdf23f8
-- 
2.43.0