gitlab-ci: Only install cmake MinGW package if needed

On MinGW, cmake requires curl which requires nghttp2 which requires
libxml2. But having a system libxml2 interferes with the Python tests
for now. Ultimately, we should use Python's os.add_dll_directory() on
Windows. I'm not sure why the current solution using PATH even works.

.gitlab-ci.yml

@@ -147,7 +147,7 @@ cmake:linux:clang:static:
   before_script:
     - "[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12"
     - $Env:Path="C:\msys64\$Env:MINGW_PATH\bin;C:\msys64\usr\bin;$Env:Path"
-    - bash -lc 'sh .gitlab-ci/setup_mingw.sh'
+    - bash -lc 'sh .gitlab-ci/setup_mingw.sh cmake ninja'
     - .gitlab-ci/Install-7-Zip
     - .gitlab-ci/Fetch-W3C-Tests
   script:

.gitlab-ci/setup_mingw.sh

@@ -1,16 +1,11 @@
 #!/bin/sh
 
+pacman --noconfirm -Syu
+
 prefix=
 if [ -n "$MINGW_PACKAGE_PREFIX" ]; then
     prefix="${MINGW_PACKAGE_PREFIX}-"
 fi
-
-pacman --noconfirm -Syu
-pacman --noconfirm -S --needed \
-    ${prefix}autotools \
-    ${prefix}cmake \
-    ${prefix}libiconv \
-    ${prefix}ninja \
-    ${prefix}python \
-    ${prefix}xz \
-    ${prefix}zlib
+for module in autotools libiconv python xz zlib "$@"; do
+    pacman --noconfirm -S --needed ${prefix}$module
+done