ci: clean build dir before case-opt pre-build; drop retry

Stale build artifacts from a previous job with a different compiler
(e.g. gfortran CPU build followed by nvfortran GPU case-opt build)
cause linker failures: undefined references to _gfortran_* symbols.

Add rm -rf build at the start of prebuild-case-optimization.sh so every
pre-build starts on a clean slate regardless of what the runner workspace
contains. This fixes the liblapack.a cross-compiler link failure.

Also remove the nick-fields/retry wrapper from the Frontier login-node
pre-build step: one clean attempt is sufficient and retries were only
masking the root cause.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/scripts/prebuild-case-optimization.sh

@@ -21,6 +21,8 @@ case "$cluster" in
     *) echo "ERROR: Unknown cluster '$cluster'"; exit 1 ;;
 esac
 
+rm -rf build
+
 . ./mfc.sh load -c "$flag" -m g
 source .github/scripts/gpu-opts.sh
 

.github/workflows/test.yml

@@ -338,13 +338,7 @@ jobs:
 
       - name: Pre-Build (login node)
         if:   matrix.cluster != 'phoenix'
-        uses: nick-fields/retry@ce71cc2ab81d554ebbe88c79ab5975992d79ba08 # v3
-        with:
-          max_attempts: 2
-          retry_wait_seconds: 60
-          timeout_minutes: 120
-          command: bash .github/scripts/prebuild-case-optimization.sh ${{ matrix.cluster }} ${{ matrix.device }} ${{ matrix.interface }}
-          on_retry_command: rm -rf build
+        run:  bash .github/scripts/prebuild-case-optimization.sh ${{ matrix.cluster }} ${{ matrix.device }} ${{ matrix.interface }}
 
       - name: Run Case-Optimization Tests
         run:  bash .github/workflows/${{ matrix.cluster }}/submit.sh .github/scripts/run_case_optimization.sh ${{ matrix.device }} ${{ matrix.interface }}