toolchain: fix multilib flags for SPARC

[lukileczo]

JIRA: RTOS-918

Description

Add PIC flags to libstdcpp only when the mulitlib requires it.
Change -fPIE multilib flag to -fPIC

Motivation and Context

libstdcpp wasn't compiled with appriopriate flags on SPARC MMU platforms.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: sparcv8leon3-generic-qemu

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[lukileczo]

@badochov could you please check if sparc NOMMU still works correctly?

[github-actions]

Unit Test Results

7 700 tests   6 985 ✅  37m 41s ⏱️
  436 suites    715 💤
    1 files        0 ❌

Results for commit b18ad0f.

♻️ This comment has been updated with latest results.

[badochov]

LGTM