ci: merge build-x86_64 & build-misc

The split doesn't really make sense anymore, and with the next commit,
the build-misc jobs would get delayed until the build-x86_64 jobs are
done, which is undesirable.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30808>

.gitlab-ci.yml

@@ -145,8 +145,7 @@ stages:
   - container
   - git-archive
   - build-for-tests
-  - build-x86_64
-  - build-misc
+  - build-only
   - code-validation
   - amd
   - amd-postmerge

.gitlab-ci/build/gitlab-ci.yml

@@ -54,7 +54,7 @@
   extends:
     - .build-linux
     - .use-debian/x86_64_build
-  stage: build-x86_64
+  stage: build-only
   variables:
     LLVM_VERSION: 15
   script:
@@ -261,7 +261,6 @@ alpine-build-testing:
   extends:
     - .meson-build
     - .use-alpine/x86_64_build
-  stage: build-x86_64
   variables:
     BUILDTYPE: "release"
     C_ARGS: >
@@ -410,7 +409,6 @@ debian-android:
 .meson-cross:
   extends:
     - .meson-build
-  stage: build-misc
   variables:
     UNWIND: "disabled"
     DRI_LOADERS: >
@@ -533,7 +531,7 @@ debian-arm64-build-test:
 debian-arm64-release:
   extends:
     - debian-arm64
-  stage: build-misc
+  stage: build-only
   variables:
     BUILDTYPE: release
     S3_ARTIFACT_NAME: mesa-arm64-default-${BUILDTYPE}