Robustify the source zip creation

- Use $$(dir) in place of $(dir), as $(call)/$(eval) eats one of the
  dollars. Previously, ./tmp was used as the temp dir
- rm -rf before and after, in case cruft is left after a build error

Bug: 151360309
Test: inspect build against with `ninja -t commands`
Change-Id: Iec891df8d5bd52ef180c46099c1107e71e4cac83
1 file changed