libstdc++ -> libiconv depenedncy: implications on in-tree libiconv

[Arsen Arsenović]

Evening!

While working on

  https://inbox.sourceware.org/20240414001113.1698685-1-arsen@aarsen.me/

I had noticed that libstdc++ currently does not get linked against an
in-tree libiconv, as the in-tree libiconv is only a host library.
Should it also be a target one?

With a quick hack of copying libiconv in the build dir as
arm64-apple-darwin21.6.0/libiconv, I had managed to get libstdc++ not to
link system libiconv.  This implies that simply enabling building iconv
as a target library also would suffice.

There are considerations with this, though:  naturally, this implies
that libstdc++ now contains a copy of libiconv as it gets linked in as a
'.a'.  It appears not to cause a copy of the symbols to be emitted on
this platform:

  cfarm104:gcc-build arsen$ objdump --syms ./aarch64-apple-darwin21.6.0/libstdc++-v3/src/.libs/libstdc++.6.dylib | grep iconv
  cfarm104:gcc-build arsen$

... however, even in that case, the symbols are renamed AFAICT:

  cfarm104:gcc-build arsen$ objdump --syms ./aarch64-apple-darwin21.6.0/libiconv/lib/.libs/libiconv.a | grep iconv
  ./aarch64-apple-darwin21.6.0/libiconv/lib/.libs/libiconv.a(iconv.o):	file format mach-o arm64
  00000000000dbbe0 g     O __DATA,__data __libiconv_version
  0000000000013730 g     F __TEXT,__text _iconv_canonicalize
  0000000000013080 g     F __TEXT,__text _libiconv
  00000000000130c0 g     F __TEXT,__text _libiconv_close
  0000000000012ca0 g     F __TEXT,__text _libiconv_open
  00000000000130e0 g     F __TEXT,__text _libiconv_open_into
  0000000000013468 g     F __TEXT,__text _libiconvctl
  00000000000135ac g     F __TEXT,__text _libiconvlist
  ./aarch64-apple-darwin21.6.0/libiconv/lib/.libs/libiconv.a(localcharset.o):	file format mach-o arm64
  ./aarch64-apple-darwin21.6.0/libiconv/lib/.libs/libiconv.a(relocatable.o):	file format mach-o arm64
  00000000000000e4 g     F __TEXT,__text _libiconv_relocate
  00000000000001e0 g     F __TEXT,__text _libiconv_relocate2
  0000000000000000 g     F __TEXT,__text _libiconv_set_relocation_prefix

... so, that might be okay?

What do you think?  Should be build a libiconv as a target lib for
libstdc++ use?

TIA, have a lovely night!
-- 
Arsen Arsenović
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