use target AR instead of host AR

[zbarnett]

Describe the contribution
Use the target ar utility instead of the host ar utility to extract objects from the binaries compiled for the target.

Testing performed
Steps taken to test the contribution:

1. Build steps '...'
2. Execution steps '...'

Expected behavior changes
A clear and concise description of how this contribution will change behavior and level of impact.

• API Change: xxx (if applicable)
• Behavior Change: xxx (if applicable)
• Or no impact to behavior

System(s) tested on

• Hardware: [e.g. PC, SP0, MCP750]
• OS: [e.g. Ubuntu 18.04, RTEMS 4.11, VxWorks 6.9]
• Versions: [e.g. cFE 6.6, OSAL 4.2, PSP 1.3 for mcp750, any related apps or tools]

Contributor Info - All information REQUIRED for consideration of pull request
Full name and company/organization/center of all contributors ("Personal" if individual work)

• If NASA Civil Servant Employee or GSFC Contractor on SES II
  • Address/email/phone and contract/task information (if applicable) must be on file