[babl] gitlab-ci: Consolidate pacman setup and cache downloaded pacman packages

[Øyvind "pippin" Kolås <ok src gnome org>]

commit 41b8019554971e00d81282729ba76be6439eb010
Author: Jan Vesely <jano vesely gmail com>
Date:   Sat May 4 22:14:26 2019 -0400

    gitlab-ci: Consolidate pacman setup and cache downloaded pacman packages
    
    Signed-off-by: Jan Vesely <jano vesely gmail com>

 .gitlab-ci.yml | 33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index bca1a79..414fc1d 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,6 +1,15 @@
+cache:
+  paths:
+    - _pacman_cache
+
 .build:
   stage: build
   image: archlinux/base:latest
+  before_script:
+    - pacman -Syu --noconfirm --needed --cachedir `pwd`/_pacman_cache
+        base-devel
+        git
+        ${EXTRA_PKGS}
 
 .meson-build:
   extends: .build
@@ -48,39 +57,21 @@ latest-meson-lcms:
   extends: .meson-build
   variables:
     LCMS_OPTION : "-Dwith-lcms=true"
-  before_script:
-    - pacman -Syu --noconfirm --needed
-        base-devel
-        meson
-        lcms2
-        git
+    EXTRA_PKGS: "lcms2 meson"
 
 latest-meson-nolcms:
   extends: .meson-build
   variables:
     LCMS_OPTION : "-Dwith-lcms=false"
-  before_script:
-    - pacman -Syu --noconfirm --needed
-        base-devel
-        meson
-        lcms2
-        git
+    EXTRA_PKGS: "meson"
 
 latest-autotools-lcms:
   extends: .autotools-build
   variables:
     LCMS_OPTION : "--with-lcms"
-  before_script:
-    - pacman -Syu --noconfirm --needed
-        base-devel
-        lcms2
-        git
+    EXTRA_PKGS: "lcms2"
 
 latest-autotools-nolcms:
   extends: .autotools-build
   variables:
     LCMS_OPTION : "--without-lcms"
-  before_script:
-    - pacman -Syu --noconfirm --needed
-        base-devel
-        git