[source] scripts: get_source_date_epoch.sh: fix mercurial support, add mtime fallback

[LEDE Commits]

jow pushed a commit to source.git, branch lede-17.01:
https://git.lede-project.org/23fd4e65bafb7856770075522111bcba3cb3b6fb

commit 23fd4e65bafb7856770075522111bcba3cb3b6fb
Author: Jo-Philipp Wich <jo at mein.io>
AuthorDate: Tue Jan 31 07:50:29 2017 +0100

    scripts: get_source_date_epoch.sh: fix mercurial support, add mtime fallback
    
    Add a fallback case to get_source_date_epoch.sh which reports the modification
    time of the script itself in case there is no SCM information available, e.g.
    when downloading .tar.gz or .zip tarballs produced by Github.
    
    Also fix the mercurial case while we're at it.
    
    Signed-off-by: Jo-Philipp Wich <jo at mein.io>
---
 scripts/get_source_date_epoch.sh | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/scripts/get_source_date_epoch.sh b/scripts/get_source_date_epoch.sh
index ea8d930..84ba445 100755
--- a/scripts/get_source_date_epoch.sh
+++ b/scripts/get_source_date_epoch.sh
@@ -17,9 +17,14 @@ try_git() {
 
 try_hg() {
 	[ -d .hg ] || return 1
-	SOURCE_DATE_EPOCH=""
+	SOURCE_DATE_EPOCH="$(hg log --template '{date}' -l 1 | cut -d. -f1)"
 	[ -n "$SOURCE_DATE_EPOCH" ]
 }
 
-try_version || try_git || try_hg || SOURCE_DATE_EPOCH=""
+try_mtime() {
+	perl -e 'print((stat $ARGV[0])[9])' "$0"
+	[ -n "$SOURCE_DATE_EPOCH" ]
+}
+
+try_version || try_git || try_hg || try_mtime || SOURCE_DATE_EPOCH=""
 echo "$SOURCE_DATE_EPOCH"