Clean stale build artifacts at start of every CI job

Self-hosted runners have persistent workspaces that accumulate build
artifacts across CI runs. When different compiler configs (e.g. gfortran
vs NVHPC) run on the same runner, stale LAPACK/dependency libraries
compiled by the wrong compiler cause linker failures. git clean -ffdx
often fails on the shared scratch filesystem (could not lstat errors),
leaving the contaminated artifacts in place.

Fix by running ./mfc.sh clean proactively at the start of every job
(Phoenix test/bench, Frontier CCE/AMD build), not just on retry.

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

Author: sbryngelson

.github/workflows/frontier/build.sh

@@ -20,6 +20,9 @@ fi
 
 . ./mfc.sh load -c f -m g
 
+# Clean stale build artifacts from previous CI runs
+./mfc.sh clean
+
 if [ "$run_bench" == "bench" ]; then
     for dir in benchmarks/*/; do
         ./mfc.sh run -v "$dir/case.py" --case-optimization -j 4 --dry-run $build_opts

.github/workflows/frontier_amd/build.sh

@@ -20,6 +20,9 @@ fi
 
 . ./mfc.sh load -c famd -m g
 
+# Clean stale build artifacts from previous CI runs
+./mfc.sh clean
+
 if [ "$run_bench" == "bench" ]; then
     for dir in benchmarks/*/; do
         ./mfc.sh run -v "$dir/case.py" --case-optimization -j 4 --dry-run $build_opts

.github/workflows/phoenix/bench.sh

@@ -1,5 +1,9 @@
 #!/bin/bash
 
+# Clean stale build artifacts from previous CI runs to prevent
+# cross-compiler contamination (e.g. gfortran LAPACK linked by NVHPC)
+./mfc.sh clean
+
 n_ranks=12
 
 echo "My interface is:" $job_interface

.github/workflows/phoenix/test.sh

@@ -1,5 +1,9 @@
 #!/bin/bash
 
+# Clean stale build artifacts from previous CI runs to prevent
+# cross-compiler contamination (e.g. gfortran LAPACK linked by NVHPC)
+./mfc.sh clean
+
 build_opts=""
 if [ "$job_device" = "gpu" ]; then
     build_opts="--gpu"