gitlab-ci: rename some scripts to be Linux-specific

macOS install trees have a different layout and package names.

.gitlab-ci.yml

@@ -403,7 +403,7 @@
 
     interruptible: true
 
-.cmake_test_unix_package: &cmake_test_unix_package
+.cmake_test_linux_package: &cmake_test_linux_package
     stage: test-ext
 
     script:
@@ -420,14 +420,13 @@
 
     interruptible: true
 
-.cmake_test_unix_external: &cmake_test_unix_external
+.cmake_test_linux_external: &cmake_test_linux_external
     stage: test-ext
 
     script:
         - *before_script_unix
         - .gitlab/ci/sccache.sh
-        # Allow the server to already be running.
-        - "sccache --start-server || :"
+        - sccache --start-server
         - sccache --show-stats
         - "$LAUNCHER build/install/bin/ctest --output-on-failure -V -S .gitlab/ci/ctest_test_external.cmake"
         - sccache --show-stats
@@ -479,7 +478,7 @@ build:centos6-release:
 test:fedora31-makefiles:
     <<:
         - *fedora31_makefiles
-        - *cmake_test_unix_package
+        - *cmake_test_linux_package
         - *linux_builder_tags_qt
     rules: *rules_settings
     dependencies:
@@ -490,7 +489,7 @@ test:fedora31-makefiles:
 test:cuda10.2-nvidia:
     <<:
         - *cuda10_2_nvidia
-        - *cmake_test_unix_package
+        - *cmake_test_linux_package
         - *linux_builder_tags_cuda
     rules: *rules_settings
     dependencies:
@@ -521,7 +520,7 @@ test:fedora31-ninja:
 test:fedora31-ninja-multi:
     <<:
         - *fedora31_ninja_multi
-        - *cmake_test_unix_external
+        - *cmake_test_linux_external
         - *linux_builder_tags_qt
     rules: *rules_settings
     dependencies: