libcxx-powerpc: can we get rid of depending on system libstdc++ completely?

[barracuda156]

So I tried to build icu against libcxx on PowerPC. Here linking failed:

/opt/local/bin/g++-mp-12 -dynamiclib -dynamic -pipe -Os -arch ppc -W -Wall -pedantic -Wpointer-arith -Wwrite-strings -Wno-long-long -std=c++11    -fvisibility=hidden -Wl,-headerpad_max_install_names -stdlib=libc++ -L/opt/local/libexec/llvm-7.1.1/lib -lc++ -arch ppc    -Wl,-compatibility_version -Wl,74 -Wl,-current_version -Wl,74.1 -install_name /opt/local/lib/libicuuc.74.dylib -o ../lib/libicuuc.74.1.dylib appendable.o bmpset.o brkeng.o brkiter.o bytesinkutil.o bytestream.o bytestrie.o bytestriebuilder.o bytestrieiterator.o caniter.o characterproperties.o chariter.o charstr.o cmemory.o cstr.o cstring.o cwchar.o dictbe.o dictionarydata.o dtintrv.o edits.o emojiprops.o errorcode.o filteredbrk.o filterednormalizer2.o icudataver.o icuplug.o loadednormalizer2impl.o localebuilder.o localematcher.o localeprioritylist.o locavailable.o locbased.o locdispnames.o locdistance.o locdspnm.o locid.o loclikely.o loclikelysubtags.o locmap.o locresdata.o locutil.o lsr.o lstmbe.o messagepattern.o mlbe.o normalizer2.o normalizer2impl.o normlzr.o parsepos.o patternprops.o pluralmap.o propname.o propsvec.o punycode.o putil.o rbbi.o rbbi_cache.o rbbidata.o rbbinode.o rbbirb.o rbbiscan.o rbbisetb.o rbbistbl.o rbbitblb.o resbund.o resbund_cnv.o resource.o restrace.o ruleiter.o schriter.o serv.o servlk.o servlkf.o servls.o servnotf.o servrbf.o servslkf.o sharedobject.o simpleformatter.o static_unicode_sets.o stringpiece.o stringtriebuilder.o uarrsort.o ubidi.o ubidi_props.o ubidiln.o ubiditransform.o ubidiwrt.o ubrk.o ucase.o ucasemap.o ucasemap_titlecase_brkiter.o ucat.o uchar.o ucharstrie.o ucharstriebuilder.o ucharstrieiterator.o uchriter.o ucln_cmn.o ucmndata.o ucnv.o ucnv2022.o ucnv_bld.o ucnv_cb.o ucnv_cnv.o ucnv_ct.o ucnv_err.o ucnv_ext.o ucnv_io.o ucnv_lmb.o ucnv_set.o ucnv_u16.o ucnv_u32.o ucnv_u7.o ucnv_u8.o ucnvbocu.o ucnvdisp.o ucnvhz.o ucnvisci.o ucnvlat1.o ucnvmbcs.o ucnvscsu.o ucnvsel.o ucol_swp.o ucptrie.o ucurr.o udata.o udatamem.o udataswp.o uenum.o uhash.o uhash_us.o uidna.o uinit.o uinvchar.o uiter.o ulist.o uloc.o uloc_keytype.o uloc_tag.o ulocale.o ulocbuilder.o umapfile.o umath.o umutablecptrie.o umutex.o unames.o unifiedcache.o unifilt.o unifunct.o uniset.o uniset_closure.o uniset_props.o unisetspan.o unistr.o unistr_case.o unistr_case_locale.o unistr_cnv.o unistr_props.o unistr_titlecase_brkiter.o unorm.o unormcmp.o uobject.o uprops.o ures_cnv.o uresbund.o uresdata.o usc_impl.o uscript.o uscript_props.o uset.o uset_props.o usetiter.o ushape.o usprep.o ustack.o ustr_cnv.o ustr_titlecase_brkiter.o ustr_wcs.o ustrcase.o ustrcase_locale.o ustrenum.o ustrfmt.o ustring.o ustrtrns.o utext.o utf_impl.o util.o util_props.o utrace.o utrie.o utrie2.o utrie2_builder.o utrie_swap.o uts46.o utypes.o uvector.o uvectr32.o uvectr64.o wintz.o -L../lib -L../stubdata -licudata -lpthread -lm 
Undefined symbols:
  "__ZSt14__once_functor", referenced from:
      __ZSt14__once_functor$non_lazy_ptr in umutex.o
     (maybe you meant: __ZSt14__once_functor$non_lazy_ptr)
  "__ZSt20__throw_system_errori", referenced from:
      __ZNSt5mutex4lockEv in umutex.o
      __ZSt9call_onceIRFvvEJEEvRSt9once_flagOT_DpOT0_ in umutex.o
      __ZNK6icu_7412UnifiedCache5_pollERKNS_12CacheKeyBaseERPKNS_12SharedObjectER10UErrorCode in unifiedcache.o
      __ZNSt5mutex4lockEv in unifiedcache.o
  "__ZNSt18condition_variable10notify_allEv", referenced from:
      __ZN6icu_7421umtx_initImplPostInitERNS_9UInitOnceE in umutex.o
      __ZNK6icu_7412UnifiedCache4_putEPK12UHashElementPKNS_12SharedObjectE10UErrorCode in unifiedcache.o
  "__ZSt16__get_once_mutexv", referenced from:
      __ZSt9call_onceIRFvvEJEEvRSt9once_flagOT_DpOT0_ in umutex.o
  "___once_proxy", referenced from:
      ___once_proxy$non_lazy_ptr in umutex.o
     (maybe you meant: ___once_proxy$non_lazy_ptr)
  "__ZNSt18condition_variableC1Ev", referenced from:
      _umtx_init in umutex.o
      __ZN6icu_7412UnifiedCache11getInstanceER10UErrorCode in unifiedcache.o
  "__ZNSt18condition_variableD1Ev", referenced from:
      _umtx_cleanup in umutex.o
      _unifiedcache_cleanup in unifiedcache.o
  "__ZSt27__set_once_functor_lock_ptrPSt11unique_lockISt5mutexE", referenced from:
      __ZSt9call_onceIRFvvEJEEvRSt9once_flagOT_DpOT0_ in umutex.o
      __ZSt9call_onceIRFvvEJEEvRSt9once_flagOT_DpOT0_ in umutex.o
      __ZSt9call_onceIRFvvEJEEvRSt9once_flagOT_DpOT0_ in umutex.o
  "__ZNSt18condition_variable4waitERSt11unique_lockISt5mutexE", referenced from:
      __ZN6icu_7420umtx_initImplPreInitERNS_9UInitOnceE in umutex.o
      __ZNK6icu_7412UnifiedCache5_pollERKNS_12CacheKeyBaseERPKNS_12SharedObjectER10UErrorCode in unifiedcache.o
ld: symbol(s) not found

Apparently these symbols are provided by libstdc++: ​https://gcc.gnu.org/legacy-ml/gcc-help/2019-12/msg00090.html

If I just add -lstdc++ to the command above, it links successfully. But to all three libraries:

36-145% otool -L /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_devel_icu/icu/work/icu/source/lib/libicuuc.74.1.dylib 
/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_devel_icu/icu/work/icu/source/lib/libicuuc.74.1.dylib:
	/opt/local/lib/libicuuc.74.dylib (compatibility version 74.0.0, current version 74.1.0)
	/opt/local/libexec/llvm-7.1.1/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1.0.0)
	/opt/local/lib/libicudata.74.dylib (compatibility version 74.0.0, current version 74.1.0)
	/opt/local/lib/libgcc/libstdc++.6.dylib (compatibility version 7.0.0, current version 7.32.0)
	/opt/local/libexec/llvm-7.1.1/lib/libc++abi.1.dylib (compatibility version 1.0.0, current version 1.0.0)
	/opt/local/lib/libgcc/libgcc_s.1.1.dylib (compatibility version 1.0.0, current version 1.1.0)
	/usr/lib/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 117.0.0)

This is likely wrong.

16. S. The issue is perhaps nothing specific to PowerPC and should be reproducible on Intel without a native libc++.