[...]

do so (now or later) by using -b with the checkout command again. Example:
  git checkout -b new_branch_name
HEAD is now at 82216f5... - updated to 2.3.9 - removed obsolete xserver-1.19 patch
fatal: HEAD does not point to a branch
Available branches: master
Searching for tag auto/ti/xorg-driver-video-savage-2.3.9-1...
Searching for tag auto/ti/xorg-driver-video-savage-2_3_9-1...
--2018-03-15 09:19:09--  http://distfiles.pld-linux.org/distfiles/by-md5/f/6/f694b2b201fb815cd3b910e639f55bb5/xf86-video-savage-2.3.9.tar.bz2
Resolving distfiles.pld-linux.org (distfiles.pld-linux.org)... 193.239.45.41
Connecting to distfiles.pld-linux.org (distfiles.pld-linux.org)|193.239.45.41|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 433686 (424K) [application/x-bzip2]
Saving to: 'xf86-video-savage-2.3.9.tar.bz2'
     0K .......... .......... .......... .......... .......... 11% 1.23M 0s
    50K .......... .......... .......... .......... .......... 23% 2.25M 0s
   100K .......... .......... .......... .......... .......... 35%  208M 0s
   150K .......... .......... .......... .......... .......... 47%  269M 0s
   200K .......... .......... .......... .......... .......... 59% 2.60M 0s
   250K .......... .......... .......... .......... .......... 70% 77.7M 0s
   300K .......... .......... .......... .......... .......... 82% 79.1M 0s
   350K .......... .......... .......... .......... .......... 94% 2.61M 0s
   400K .......... .......... ...                             100%  254M=0.1s
2018-03-15 09:19:09 (4.11 MB/s) - 'xf86-video-savage-2.3.9.tar.bz2' saved [433686/433686]
Building target platforms: i686-linux
Wrote: /home/users/builder/rpm/SRPMS/xorg-driver-video-savage-2.3.9-1.src.rpm
exit status 0
Tagging with prefix: auto/ti/
HEAD is now at 82216f5... - updated to 2.3.9 - removed obsolete xserver-1.19 patch
fatal: HEAD does not point to a branch
Writing git revision for tag auto/ti/xorg-driver-video-savage-2.3.9-1
On detached HEAD. Use -r BRANCHNAME to override
error: Macro %_builddir has empty body
error: Macro %_builddir has empty body
Executing(--clean): env -i TMP=/home/users/builder/tmp HOME=/home/users/builder PATH=/bin:/usr/bin:/usr/sbin:/sbin:/usr/X11R6/bin TMPDIR=/home/users/builder/tmp  /bin/sh -e /home/users/builder/tmp/rpm-tmp.26147
+ umask 022
+ cd /home/users/builder/rpm/BUILD
+ rm -rf xf86-video-savage-2.3.9
Begin-TLD-Builder-Info
Build-Time: user:0.53s sys:0.11s real:2.08s (faults io:0 non-io:91948)
Files queued for ftp:
    440217 xorg-driver-video-savage-2.3.9-1.src.rpm
       202 xorg-driver-video-savage-2.3.9-1.src.rpm.uploadinfo
End-TLD-Builder-Info