use private fields in pkgconfig files

- use `Requires.private` in pkgconfig files to stop forcing downstream
  packages to link against everything upstream
- added `pkgconfig` as `BuildRequires` for RPMs
- bumped required version of pkg-config to 0.18.0
23 jobs for pkgconfig-private in 31 minutes and 25 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Level0
passed #333641
level0:gstlal

00:02:44

passed #333646
allowed to fail
level0:rpm:gstlal

00:01:30

failed #333624
level0:gstlal

00:02:55

failed #333623
allowed to fail
level0:rpm:gstlal

00:02:56

 
  Level1
passed #333626
level1:gstlal-ugly

00:02:39

passed #333647
allowed to fail
level1:rpm:gstlal-ugly

00:01:51

failed #333625
allowed to fail
level1:rpm:gstlal-ugly

00:00:22

 
  Level2
passed #333648
level2:gstlal-burst

00:00:32

passed #333649
level2:gstlal-calibration

00:02:57

passed #333650
level2:gstlal-inspiral

00:03:18

passed #333651
allowed to fail
level2:rpm:gstlal-burst

00:00:44

passed #333652
allowed to fail
level2:rpm:gstlal-calibration

00:01:33

passed #333653
allowed to fail
level2:rpm:gstlal-inspiral

00:03:35

failed #333632
level2:gstlal-burst

00:01:13

failed #333630
level2:gstlal-calibration

00:01:13

failed #333631
level2:gstlal-inspiral

00:01:14

failed #333629
allowed to fail
level2:rpm:gstlal-burst

00:01:11

failed #333628
allowed to fail
level2:rpm:gstlal-calibration

00:00:24

failed #333627
allowed to fail
level2:rpm:gstlal-inspiral

00:00:25

 
  Test Gstlal
passed #333633
test:gstlal

00:00:20

 
  Test Inspiral
passed #333634
allowed to fail
test:gstlal-inspiral

00:00:33

 
  Test Burst
passed #333635
allowed to fail
test:gstlal-burst

00:00:15

 
  Test Offline
passed #333636
allowed to fail
test:offline

00:16:09