Use a better method of fixing up Verific run-test.mk

Author: akashlevy

tests/verific/run-test.sh

@@ -2,4 +2,4 @@
 set -eu
 source ../gen-tests-makefile.sh
 generate_mk --yosys-scripts --bash
-sed -i '1i\export ASAN_OPTIONS=halt_on_error=0' run-test.mk
+echo "$(echo 'export ASAN_OPTIONS=halt_on_error=0'; cat run-test.mk)" > run-test.mk