difficulty building gcc 4.6.3 on MacOS

[scs at eskimo dot com (Steve Summit)]

I'm trying to build gcc 4.6.3 on MacOS 10.9.5 (Mavericks).
The first-stage compiler builds fine, but it dies on a support
library build.  Specifically, when trying to build libgcc_s.dylib,
it fails because ld can't find -ldylib1.10.5.o .  (Transcript
excerpt appended below.)

I see that libdylib1.10.5.o on this system is hiding down
underneath /Applications/Xcode.app, but it doesn't look like the
stage-1 xgcc is being invoked with a -L argument that would find
it there.  I've tried configuring --with-stage1-ldflags=-L...
(filling in the whole contorted path), but doesn't help; in fact
the particular build step that's failing doesn't seem to be
making use of the --with-stage1-ldflags configuration at all.

The problem may stem from combining an older version of gcc with
a newer version of MacOS; a newer version of gcc might work fine.
I'm building this version of gcc as a prelude to building a
cross-compiler which targets 4.6.3 for compatibility reasons, but
if 4.6.3 is impossible on this system I may have to change course.

I may need to create symlinks to make the libraries underneath
/Applications/Xcode.app easier to find, e.g. via /usr/local/lib/.
(For my own convenience I had already creeated a symlink
/usr/include pointing to Xcode's standard headers hiding
underneath /Applications/Xcode.app, and I suspect that symlink
ended up helping earlier steps in the gcc build succeed.)

Any suggstions for diagnosing or fixing this situation appreciated.

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Transcript of the step that's failing:

# @multilib_dir@ is not really necessary, but sometimes it has
# more uses than just a directory name.
/bin/sh /Users/scs/projs/gcc/gcc-4.6.3-obj/../gcc-4.6.3/libgcc/../mkinstalldirs i386
mkdir i386
/Users/scs/projs/gcc/gcc-4.6.3-obj/./gcc/xgcc -B/Users/scs/projs/gcc/gcc-4.6.3-obj/./gcc/ -B/usr/local/x86_64-apple-darwin13.4.0/bin/ -B/usr/local/x86_64-apple-darwin13.4.0/lib/ -isystem /usr/local/x86_64-apple-darwin13.4.0/include -isystem /usr/local/x86_64-apple-darwin13.4.0/sys-include    -O2  -g -O2 -DIN_GCC   -W -Wall -Wwrite-strings -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include  -fPIC -pipe -g -DHAVE_GTHR_DEFAULT -DIN_LIBGCC2 -D__GCC_FLOAT_NOT_NEEDED -fno-stack-protector  -dynamiclib -nodefaultlibs -install_name /usr/local/lib/libgcc_s.1.dylib -single_module -o i386/libgcc_s.dylib -Wl,-exported_symbols_list,libgcc.map -compatibility_version 1 -current_version 1.0 -g -O2 -m32 -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 _enable_execute_stack_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 _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 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 extendsftf2_s.o extenddftf2_s.o extendxftf2_s.o trunctfsf2_s.o trunctfdf2_s.o trunctfxf2_s.o tf-signs_s.o unwind-dw2_s.o unwind-dw2-fde-darwin_s.o unwind-sjlj_s.o unwind-c_s.o emutls_s.o -lc
ld: library not found for -ldylib1.10.5.o
collect2: ld returned 1 exit status
make[5]: *** [libgcc_s.dylib] Error 1
make[4]: *** [multi-do] Error 1
make[3]: *** [all-multi] Error 2
make[2]: *** [all-stage1-target-libgcc] Error 2
make[1]: *** [stage1-bubble] Error 2