Update build.sh to pass shellcheck checks

[ia]

• Please check if the PR fulfills these requirements

• The changes have been tested locally
• There are no breaking changes

• What kind of change does this PR introduce?
  Update build.sh according to shellcheck recommendations.

• What is the current behavior?
  There are four warnings for build.sh currently.

• What is the new behavior (if this is a feature change)?
  Update build.sh to remove shellcheck warnings.

• Other information:
  I know that IFS without read should be ok but since shellcheck complains about checking arrays why wouldn't update those two as well.