Support build of projects outside of beats directory (#36126)

* Add project dir

* Remove comments

* Add changelog

CHANGELOG.next.asciidoc

@@ -74,6 +74,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 - Fix recovering from invalid output configuration when running under Elastic-Agent {pull}36016[36016]
 - Improve StreamBuf append to improve performance when reading long lines from files. {pull}35928[35928]
 - Eliminate cloning of event in deepUpdate {pull}35945[35945]
+- Support build of projects outside of beats directory {pull}36126[36126]
 
 *Auditbeat*
 

dev-tools/mage/build.go

@@ -139,6 +139,18 @@ func GolangCrossBuild(params BuildArgs) error {
 		return err
 	}
 
+	// Support projects outside of the beats directory.
+	repoInfo, err := GetProjectRepoInfo()
+	if err != nil {
+		return err
+	}
+
+	// TODO: Support custom build dir/subdir
+	projectMountPoint := filepath.ToSlash(filepath.Join("/go", "src", repoInfo.CanonicalRootImportPath))
+	if err := sh.Run("git", "config", "--global", "--add", "safe.directory", projectMountPoint); err != nil {
+		return err
+	}
+
 	return Build(params)
 }