I'm now able to build the interpreter (and run it in qemu on the same machine), but building the extension modules fails. the build is configured as:

CC="arm-linux-gnueabihf-gcc" \
CXX="arm-linux-gnueabihf-g++" \
CFLAGS="-g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Wformat-security -Werror=format-security" \
LDFLAGS="-Wl,-Bsymbolic-functions -Wl,-z,relro" \
    ../cross/configure \
        --prefix=/usr \
        --enable-ipv6 \
        --with-computed-gotos \
        --enable-loadable-sqlite-extensions \
        --with-dbmliborder=bdb:gdbm \
        --with-system-expat \
        --with-system-ffi \
        --with-fpectl \
        --host=arm-linux-gnueabihf \
        --build=x86_64-linux-gnu

building 'cmath' extension
arm-linux-gnueabihf-gcc -fPIC -Wno-unused-result -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -fstack-protector --param=ssp-buffer-size=4 -Wformat -Wformat-security -Werror=format-security -I. -I/usr/include/arm-linux-gnueabihf -I/usr/local/include -I/usr/include/python3.3m -c cmathmodule.c -o build/temp.linux-x86_64-3.3/cmathmodule.o
arm-linux-gnueabihf-gcc: error: cmathmodule.c: No such file or directory
arm-linux-gnueabihf-gcc: fatal error: no input files
compilation terminated.

the source files are not found (srcdir != builddir), the patch from rpetrov talks about:

+# revert patch from issue 7880 :
+#  - the test case (from issue 7880) works for me
+#  - realpath break cross compilation
+# => so lets use abspath again ;)
+# NOTE "Issue #6612: Fix site and sysconfig to catch os.getcwd() error,
+# eg. if the current directory was deleted." replase all occurrence of
+# realpath with _safe_realpath. Instead to update _safe_realpath to use
+# abspath the cross-compilation revert all!

but I'm running out of time, and won't work on this for the next two weeks.