Guard IEEE halting on macOS flang

[mathomp4]

Summary

• Guard IEEE halting mode calls on macOS flang to avoid missing fe*except symbols during MPI initialization.
• Update changelog with the macOS flang workaround.
• Note ongoing flang test instability on macOS (see issue MAPL tests segfault on macOS flang (signal 11, invalid permissions) #4473).

Testing

• make MAPL.cap VERBOSE=1
• make -j4 install
• make -j4 tests (fails on macOS flang: MAPL.state.tests and MAPL.base.tests segfault; signal 11, invalid permissions)

[tclune]

Presumably something similar will be needed for cap3g.

[mathomp4]

Presumably something similar will be needed for cap3g.

Ah true. Let me try a MAPL3 build as well.

[mathomp4]

Presumably something similar will be needed for cap3g.

Ah true. Let me try a MAPL3 build as well.

@tclune Huh. The answer seems to be... no? There is no MPI_Init_thread call in MAPL3 other than in pfio demo programs.

Indeed, there are no MPI_Init calls outside of demo/benchmark/test programs.

[tclune]

In MAPL3 we are returning to letting ESMF launch MPI for us. Hopefully this issue won't force us back.