gcc 4.7.3 build error. How to resolve gcc bootstrap error "Where has _float128 gone?"

[David Johnson]

I am trying to install gcc 4.7.3 or greater. The specs of my machine are 
as follows.

     OS X 10.8.4
     Darwin 12.4.0

     gcc 4.2.1, configured with:

     --disable-checking
     --enable-werror
--prefix=/Applications/Xcode.app/Contents/Developer/usr/llvm-gcc-4.2
     --mandir=/share/man
     --enable-languages=c,objc,c++,obj-c++
     --program-prefix=llvm-
     --program-transform-name=/^[cg][^.-]*$/s/$/-4.2/
     --with-slibdir=/usr/lib
     --build=i686-apple-darwin11
--enable-llvm=/private/var/tmp/llvmgcc42/llvmgcc42-2336.11~28/dst-llvmCore/Developer/usr/local
     --program-prefix=i686-apple-darwin11-
     --host=x86_64-apple-darwin11
     --target=i686-apple-darwin11
     --with-gxx-include-dir=/usr/include/c++/4.2.1

I have performed the following steps thus far.

$ tar zxf gcc-4.7.3.tar.gz
$ mkdir objdir4.7.3
$ cd objdir4.7.3
$ /Users/DJ/gcc-4.7.3/configure
$ make bootstrap

This produces the following error

In file included from ./kinds.h:75:0,
              from 
/Users/DJ/scratch/gcc-4.7.3/libgfortran/libgfortran.h:232,
              from /Users/DJ/scratch/gcc-4.7.3/libgfortran/fmain.c:4:
/Users/DJ/scratch/gcc-4.7.3/libgfortran/kinds-override.h:40:5: error: 
#error "Where has __float128 gone?"
make[3]: *** [fmain.lo] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all-target-libgfortran] Error 2
make: *** [bootstrap] Error 2

I have tried implementing the fix found here: 
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53731

I implemented this fix by first deleting everything in the objdir4.7.3 
directory and then modifying .../gcc-4.7.3/Makefile.in and 
.../gcc-4.7.3/Makfile.tpl as described in the fix. The fix required 
adding (MULTISUBDIR) in one place in each file. I saved these changes as 
a patched version in a new directory called .../gcc-4.7.3_patched.

I cd'ed into the objdir4.7.3 directory once more and then ran the 
configure script in the pathed directory. The make bootstrap step 
resulted in the same error.