remove linux-specific mktemp usage (#1571)

(cherry picked from commit 7361ffd2)

scripts/build.sh

@@ -7,7 +7,8 @@ set -o errexit
 rm -rf build
 
 # Create a temporary directory to place ignored files (e.g. examples).
-tmp_dir="$(mktemp -dp.)"
+tmp_dir="ignored_contracts"
+mkdir "$tmp_dir"
 
 # Move the ignored files to the temporary directory.
 while IFS="" read -r ignored