build: avoid git repository discovery when determining version

When attempting to use Git to populate commit/branch information in a
version string, it is possible through repository discovery that it
uses Git information not relevant to project. For example, if
repository content is extract into an interim build location when using
an embedded build framework (e.g. Buildroot), the project will not have
its Git repository to refer to. When it cannot find its repository, it
will look into its parent folders and may find the Git repository of
another project and use its branch/commit information.

This commit provides an explicit path to the project's Git repository
when consider commit/branch information. This will prevent any
repository discovery from occurring.

Signed-off-by: James Knight <james.d.knight@live.com>

meson.build

@@ -160,8 +160,8 @@ add_project_arguments('-DSYSCONFDIR="/@0@"'.format(join_paths(prefix, sysconfdir
 version = '"@0@"'.format(meson.project_version())
 git = find_program('git', native: true, required: false)
 if git.found()
-	git_commit = run_command([git, 'rev-parse', '--short', 'HEAD'], check: false)
-	git_branch = run_command([git, 'rev-parse', '--abbrev-ref', 'HEAD'], check: false)
+	git_commit = run_command([git, '--git-dir=.git', 'rev-parse', '--short', 'HEAD'], check: false)
+	git_branch = run_command([git, '--git-dir=.git', 'rev-parse', '--abbrev-ref', 'HEAD'], check: false)
 	if git_commit.returncode() == 0 and git_branch.returncode() == 0
 		version = '"@0@-@1@ (" __DATE__ ", branch \'@2@\')"'.format(
 			meson.project_version(),