fix: use stat -hierarchy for hierarchical synth to report area

When SYNTH_HIERARCHICAL=1, the yosys stat command reports zero area
for the top module because all cells are in submodules. Adding
-hierarchy makes stat include submodule area, so
synth__design__instance__area__stdcell is no longer N/A.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>

Author: oharboe

flow/scripts/synth.tcl

@@ -226,7 +226,11 @@ if { $::env(SYNTH_INSBUF) } {
 # Reports
 tee -o $::env(REPORTS_DIR)/synth_check.txt check
 
-tee -o $::env(REPORTS_DIR)/synth_stat.txt stat {*}$lib_args
+if { $::env(SYNTH_HIERARCHICAL) } {
+  tee -o $::env(REPORTS_DIR)/synth_stat.txt stat -hierarchy {*}$lib_args
+} else {
+  tee -o $::env(REPORTS_DIR)/synth_stat.txt stat {*}$lib_args
+}
 
 # check the design is composed exclusively of target cells, and
 # check for other problems