These directions should work for Python 2.7.x (last tested with 2.7.5).
First, uncompress Python into two separate directories, one for native and one for JavaScript.
In the JavaScript directory, do:
EMCONFIGURE_JS=1 emconfigure ./configure --without-threads --without-pymalloc --enable-shared --disable-ipv6
If you are on Mac OS X, you will also want disable-toolbox-glue.
If you are on an older version of Python (such as 2.7.2), you may
not need the --disable-ipv6 option.
If you are on Python 2.7.4 or later, you will need to edit the
Makefile generated and remove the MULTIARCH= line(s).
You will also need to edit pyconfig.h and remove defines
for DOUBLE_IS_BIG_ENDIAN_IEEE754, DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754,
and HAVE_GCC_ASM_FOR_X87.
On Python 2.7.2, you will need to edit pyconfig.h and remove
HAVE_GCC_ASM_FOR_X87, HAVE_SIG* except for SIGNAL_H
and add #define PY_NO_SHORT_FLOAT_REPR.
Now, you can run make. It will fail trying to run pgen.
At this point, go to your native directory and run:
./configure --without-threads --without-pymalloc --enable-shared --disable-ipv6
Now, run make in the native directory and then copy the generated Parser/pgen
to your JavaScript directory. Back in your JavaScript directory, be sure to flag
the pgen executable as executable:
chmod +x Parser/pgen
Now, run make again.
You will get an error about trying to run python or python.exe. This
can be ignored.
Now, you can link the bitcode file that you need:
llvm-link libpython2.7.so Modules/python.o -o python.bc
If you are on Mac OS X, you will want to look for libpython2.7.dylib
instead of libpython2.7.so.
Thanks to rasjidw and everyone else who has helped with this!