Add build verification and diagnostics

Verify libraries are built successfully and show what was actually
produced if builds fail to create expected artifacts.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/benchmarks/branch-prediction/compare_branch_prediction.sh

@@ -142,11 +142,29 @@ main() {
     cd "${BASELINE_WORKTREE}"
     ./gradlew ddprof-lib:build -x test
 
+    # Verify baseline library was built
+    local baseline_lib_check="${BASELINE_WORKTREE}/ddprof-lib/build/lib/main/release/linux/x64/libjavaProfiler.so"
+    if [ ! -f "${baseline_lib_check}" ]; then
+        log_error "Baseline build did not produce library at ${baseline_lib_check}"
+        log_info "Checking what was built:"
+        find "${BASELINE_WORKTREE}/ddprof-lib/build" -name "*.so" -type f 2>/dev/null || true
+        exit 1
+    fi
+
     # Build optimized
     log_step "4/6: Building optimized version..."
     cd "${OPTIMIZED_WORKTREE}"
     ./gradlew ddprof-lib:build -x test
 
+    # Verify optimized library was built
+    local optimized_lib_check="${OPTIMIZED_WORKTREE}/ddprof-lib/build/lib/main/release/linux/x64/libjavaProfiler.so"
+    if [ ! -f "${optimized_lib_check}" ]; then
+        log_error "Optimized build did not produce library at ${optimized_lib_check}"
+        log_info "Checking what was built:"
+        find "${OPTIMIZED_WORKTREE}/ddprof-lib/build" -name "*.so" -type f 2>/dev/null || true
+        exit 1
+    fi
+
     # Test baseline
     log_step "5/6: Testing baseline version..."
     local baseline_test_script="${OPTIMIZED_WORKTREE}/ddprof-lib/benchmarks/branch-prediction/test_branch_prediction_perf.sh"