iosbuild: output autoconf req. on failure

Change-Id: I2a6d80cf22f5b58e80345a411c48f047fecdbb47
iosbuild: cleanup

- s/declare -r/readonly/
- remove unnecessary build variables
- echo configure line

Change-Id: I4489d8413934dcec57d60abf136a72d08fa0fd99
Merge "iosbuild: output autoconf req. on failure"
Merge "iosbuild: cleanup"