Get rid of GCC false -Wmissing-noreturn warnings; remove unnecessary warning suppression code

[leekillough]

This adds DISABLE_WARN_MISSING_NORETURN, to address GCC -Wmissing-noreturn false warnings introduced by recent PRs. It is only needed in .cc files which define virtual functions which do not return; it is not needed in .h files and there is no change needed for the virtual function declarations.

GCC (but not Clang) has a bug where -Wmissing-noreturn warnings are printed for virtual functions defined outside of class which call [[noreturn]] functions but are not themselves marked [[noreturn]]. [[noreturn]] is a function attribute, not a type attribute, and is not inherited. A call to a virtual function with dynamic dispatch cannot be considered [[noreturn]] even if its declarations are marked [[noreturn]], because it can be overriden with a function which is not [[noreturn]], and a virtual function should not be warned about not being marked [[noreturn]] even if it calls a [[noreturn]] function, because [[noreturn]] adds no value to a virtual function and only serves to remove a false warning. There is discussion here, here and here.

This also removes some warning suppression methods which are now unnecessary:

1. UNUSED() macro can suppress warnings about unused variables and function parameters
2. It is not necessary to return dummy values from functions after Output::fatal() is called, since it is now marked [[noreturn]]

[github-actions]

CLANG-FORMAT TEST - PASSED

[github-actions]

CMAKE-FORMAT TEST - PASSED

[sst-autotester]

Status Flag 'Pre-Test Inspection' - - This Pull Request Requires Inspection... The code must be inspected by a member of the Team before Testing/Merging
NO INSPECTION HAS BEEN PERFORMED ON THIS PULL REQUEST! - This PR must be inspected by setting label 'AT: PRE-TEST INSPECTED'.

[sst-autotester]

Status Flag 'Pre-Test Inspection' - SUCCESS: The last commit to this Pull Request has been INSPECTED by label AT: PRE-TEST INSPECTED! Autotester is Removing Label; this inspection will remain valid until a new commit to source branch is performed.

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Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements

• Build Num: 2060
• Status: STARTED

Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements_MR-2

• Build Num: 2016
• Status: STARTED

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Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements_MT-2

• Build Num: 2015
• Status: STARTED

Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-core_Make-Dist

• Build Num: 798
• Status: STARTED

Build Information

Test Name: SST__AutotestGen2_NewFW_OSX-14-XC15-ARM2_OMPI-4.1.6_PY3.10_sst-elements

• Build Num: 572
• Status: STARTED

Using Repos:

Repo: CORE (leekillough/sst-core)

• Branch: noreturn
• SHA: c83e6aa
• Mode: TEST_REPO

Repo: SQE (sstsimulator/sst-sqe)

• Branch: devel
• SHA: a476e437d8eeb4c8330a9af35322dca689c4cec4
• Mode: SUPPORT_REPO

Repo: ELEMENTS (sstsimulator/sst-elements)

• Branch: devel
• SHA: 8ab6dcc60207adc5b8be6775e2675dc2a031da89
• Mode: SUPPORT_REPO

Repo: MACRO (sstsimulator/sst-macro)

• Branch: devel
• SHA: 31e2c16aa4d07b502bcd9c97b1872a0329ed0b38
• Mode: SUPPORT_REPO

Pull Request Author: leekillough

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Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements

• Build Num: 2060
• Status: PASSED

Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements_MR-2

• Build Num: 2016
• Status: PASSED

Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-elements_MT-2

• Build Num: 2015
• Status: PASSED

Build Information

Test Name: SST__AutotestGen2_NewFW_sst-test_OMPI-4.1.4_PY3.6_sst-core_Make-Dist

• Build Num: 798
• Status: PASSED

Build Information

Test Name: SST__AutotestGen2_NewFW_OSX-14-XC15-ARM2_OMPI-4.1.6_PY3.10_sst-elements

• Build Num: 572
• Status: PASSED

[sst-autotester]

Status Flag 'Pre-Merge Inspection' - SUCCESS: The last commit to this Pull Request has been INSPECTED AND APPROVED by [ feldergast ]!

[sst-autotester]

Status Flag 'Pull Request AutoTester' - Pull Request MUST BE MERGED MANUALLY BY Project Team - This Repo does not support Automerge

[sst-autotester]

Status Flag 'Pull Request AutoTester' - Pull Request MUST BE MERGED MANUALLY BY Project Team - This Repo does not support Automerge

[leekillough]

GCC bug submitted:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120300