The attached patch is version 2 of the SHF_GNU_RETAIN patch that was
previously discussed here:
https://sourceware.org/pipermail/binutils/2020-September/113406.html

The following changes have been made:
- Removed the .retain directive
- The assembler will create different input sections for sections with
  the same name but SHF_GNU_RETAIN set/unset (thanks to H.J. for that).
  This means the linker will be able to do a better job garbage
  collecting input sections, as the "retain" attribute applied to a
  symbol declaration in the source code will not cause other parts of
  the program that are not required, but are in the same section, to be
  unnecessarily retained.
- Added GNU OSABI handling (also thanks to H.J.).

I've successfully regtested the patch for the Binutils, GAS and LD
testsuites for the following targets:

aarch64-elf arc-elf arm-eabi arm-elf avr-elf bfin-elf cr16-elf cris-elf
crx-elf csky-elf d10v-elf d30v-elf dlx-elf epiphany-elf fr30-elf frv-elf
ft32-elf h8300-elf hppa-elf i386-elf ip2k-elf iq2000-elf lm32-elf
m32c-elf m32r-elf m68hc11-elf m68hc12-elf m68k-elf mcore-elf mep-elf
metag-elf microblaze-elf mips-elf moxie-elf msp430-elf mt-elf nios2-elf
or1k-elf pj-elf ppc-elf pru-elf riscv-elf rl78-elf rx-elf s12z-elf
score-elf sh-elf sparc-elf spu-elf tic6x-elf tilegx-elf tilepro-elf
v850-elf visium-elf wasm32-elf xgate-elf xstormy16-elf xtensa-elf
z80-elf.

The new tests only run for the targets that use the GNU OSABI. From the
above list, arm-elf, hppa-elf, msp430-elf, visium-elf do not use the GNU
OSABI, so do not support SHF_GNU_RETAIN.

Ok to apply?

Thanks,
Jozef