ci: Use set -e in frontend compiler wrapper scripts.

I doubt the shebang line in the backend script has any effect now,
since the frontend scripts just source it directly.

v2:
* Use "set -e" instead of adding -e to shebang (Eric Engestrom)

v3:
* Apply to the clang wrapper scripts as well (Eric Engestrom)

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22438>

.gitlab-ci/build/compiler-wrapper-clang++.sh

@@ -1,3 +1,6 @@
 #!/bin/sh
+
+set -e
+
 _COMPILER=clang++
 . compiler-wrapper.sh