[Darwin] Amend section for constants with reloactions.
Darwin's linker doesn't like text section relocations (they require special
enabling). At least, the Fortran FE seems to generate cases where the
initialiser for a pointer constant can need a relocation. We can handle
this by special-casing SECCAT_RODATA when the relocation is present by
placing the constant in the .const_data section.
gcc/ChangeLog:
2019-10-05 Iain Sandoe <iain@sandoe.co.uk>
PR target/59888
* config/darwin.c (darwin_rodata_section): Add relocation flag,
choose const_data section for constants with relocations.
(machopic_select_section): Pass relocation flag to
darwin_rodata_section ().
From-SVN: r276623