libgcc @6.1.0: ld: warning: could not create compact unwind for __Unwind_RaiseException: non-standard register 0 being saved in prolog

[mndavidoff (Monte Davidoff)]

Building the libgcc port fails with the following error. The problem might be related to the recent upgrades to cctools 886, ld64-latest @264.3.102, or libmacho-headers 886.

$ sudo port -vs install libgcc
...
/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/libgcc/work/build/./gcc/xgcc -B/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/libgcc/work/build/./gcc/ -B/opt/local/x86_64-apple-darwin15/bin/ -B/opt/local/x86_64-apple-darwin15/lib/ -isystem /opt/local/x86_64-apple-darwin15/include -isystem /opt/local/x86_64-apple-darwin15/sys-include    -O2  -g -O2 -pipe -Os -DIN_GCC    -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wno-format -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include   -pipe -fno-common -g -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector  -dynamiclib -nodefaultlibs -install_name /opt/local/lib/libgcc/libgcc_s.1.dylib -single_module -o ./libgcc_s.dylib -Wl,-exported_symbols_list,libgcc.map -compatibility_version 1 -current_version 1.0 -g -O2 -pipe -Os -B./ _muldi3_s.o _negdi2_s.o _lshrdi3_s.o _ashldi3_s.o _ashrdi3_s.o _cmpdi2_s.o _ucmpdi2_s.o _clear_cache_s.o _trampoline_s.o __main_s.o _absvsi2_s.o _absvdi2_s.o _addvsi3_s.o _addvdi3_s.o _subvsi3_s.o _subvdi3_s.o _mulvsi3_s.o _mulvdi3_s.o _negvsi2_s.o _negvdi2_s.o _ctors_s.o _ffssi2_s.o _ffsdi2_s.o _clz_s.o _clzsi2_s.o _clzdi2_s.o _ctzsi2_s.o _ctzdi2_s.o _popcount_tab_s.o _popcountsi2_s.o _popcountdi2_s.o _paritysi2_s.o _paritydi2_s.o _powisf2_s.o _powidf2_s.o _powixf2_s.o _powitf2_s.o _mulsc3_s.o _muldc3_s.o _mulxc3_s.o _multc3_s.o _divsc3_s.o _divdc3_s.o _divxc3_s.o _divtc3_s.o _bswapsi2_s.o _bswapdi2_s.o _clrsbsi2_s.o _clrsbdi2_s.o _fixunssfsi_s.o _fixunsdfsi_s.o _fixunsxfsi_s.o _fixsfdi_s.o _fixdfdi_s.o _fixxfdi_s.o _fixunssfdi_s.o _fixunsdfdi_s.o _fixunsxfdi_s.o _floatdisf_s.o _floatdidf_s.o _floatdixf_s.o _floatundisf_s.o _floatundidf_s.o _floatundixf_s.o _fixsfti_s.o _fixdfti_s.o _fixxfti_s.o _fixtfti_s.o _fixunssfti_s.o _fixunsdfti_s.o _fixunsxfti_s.o _fixunstfti_s.o _floattisf_s.o _floattidf_s.o _floattixf_s.o _floattitf_s.o _floatuntisf_s.o _floatuntidf_s.o _floatuntixf_s.o _floatuntitf_s.o _divdi3_s.o _moddi3_s.o _udivdi3_s.o _umoddi3_s.o _udiv_w_sdiv_s.o _udivmoddi4_s.o darwin-64_s.o cpuinfo_s.o sfp-exceptions_s.o addtf3_s.o divtf3_s.o eqtf2_s.o getf2_s.o letf2_s.o multf3_s.o negtf2_s.o subtf3_s.o unordtf2_s.o fixtfsi_s.o fixunstfsi_s.o floatsitf_s.o floatunsitf_s.o fixtfdi_s.o fixunstfdi_s.o floatditf_s.o floatunditf_s.o fixtfti_s.o fixunstfti_s.o floattitf_s.o floatuntitf_s.o extendsftf2_s.o extenddftf2_s.o extendxftf2_s.o trunctfsf2_s.o trunctfdf2_s.o trunctfxf2_s.o enable-execute-stack_s.o unwind-dw2_s.o unwind-dw2-fde-darwin_s.o unwind-sjlj_s.o unwind-c_s.o emutls_s.o libgcc.a -lc
ld: warning: could not create compact unwind for __Unwind_RaiseException: non-standard register 0 being saved in prolog
ld: warning: could not create compact unwind for __Unwind_ForcedUnwind: non-standard register 0 being saved in prolog
ld: warning: could not create compact unwind for __Unwind_Resume: does not use RBP or RSP based frame
ld: warning: could not create compact unwind for __Unwind_Resume_or_Rethrow: non
-standard register 0 being saved in prolog
collect2: fatal error: /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_gcc6/libgcc/work/build/./gcc/nm returned 2 exit status
compilation terminated.

[ryandesign (Ryan Carsten Schmidt)]

Duplicate of #51789.