meson: fix git ls-files invocations during rebase

Normally ls-files prints the full path to files from the repo root. But when
$GIT_WORK_TREE is set, ls-files prints paths relative to the current
directory. When rebasing, $GIT_WORK_TREE is set in the commands executed from
'rebase -x'. This causes problems if meson config is touched and the meson
reconfigures itself. ($GIT_WORK_TREE shouldn't be relevant, since the paths that
ls-files reports don't depend on the work tree, but whatever.) Let's unset
GIT_WORK_TREE to avoid the issue.

$ (cd test; git --git-dir=$PWD/../.git ls-files ':/test/dmidecode-dumps/*.bin')
test/dmidecode-dumps/HP-Z600.bin
test/dmidecode-dumps/Lenovo-ThinkPad-X280.bin
test/dmidecode-dumps/Lenovo-Thinkcentre-m720s.bin

$ (cd test; GIT_WORK_TREE=$PWD/.. git --git-dir=$PWD/../.git ls-files ':/test/dmidecode-dumps/*.bin')
dmidecode-dumps/HP-Z600.bin
dmidecode-dumps/Lenovo-ThinkPad-X280.bin
dmidecode-dumps/Lenovo-Thinkcentre-m720s.bin

Fixes #18148.

meson.build

@@ -3651,10 +3651,11 @@ endforeach
 
 if git.found()
         all_files = run_command(
+                'env', '-u', 'GIT_WORK_TREE',
                 git,
-                ['--git-dir=@0@/.git'.format(project_source_root),
-                 'ls-files',
-                 ':/*.[ch]'])
+                '--git-dir=@0@/.git'.format(project_source_root),
+                'ls-files', ':/*.[ch]')
+
         all_files = files(all_files.stdout().split())
 
         custom_target(

test/fuzz/meson.build

@@ -23,9 +23,10 @@ sanitizers = [['address,undefined', sanitize_address_undefined]]
 
 if git.found()
         out = run_command(
+                'env', '-u', 'GIT_WORK_TREE',
                 git,
                 '--git-dir=@0@/.git'.format(project_source_root),
-                 'ls-files', ':/test/fuzz/*/*')
+                'ls-files', ':/test/fuzz/*/*')
 else
         out = run_command(
                 'sh', '-c', 'ls @0@/test/fuzz/*/*'.format(project_source_root))

test/meson.build

@@ -142,6 +142,7 @@ if want_tests != 'false' and dmi_arches.contains(host_machine.cpu_family())
 
         if git.found()
                 out = run_command(
+                        'env', '-u', 'GIT_WORK_TREE',
                         git,
                         '--git-dir=@0@/.git'.format(project_source_root),
                         'ls-files', ':/test/dmidecode-dumps/*.bin')