setup.py assumes as(1) is used during build which isn't true. It's only
used if $CXX actually calls it and clang by default doesn't.

Equivalent issue existed in security/cryptopp and fixed in ports/154325.

How-To-Repeat: # patch-setup.py fixes the following error
$ make
[...]
clang -DNDEBUG -O2 -pipe -fPIC -I. -I/usr/local/include/python2.7 -c embeddedcryptopp/sosemanuk.cpp -o temp.freebsd-10-amd64-2.7/embeddedcryptopp/sosemanuk.o -w
embeddedcryptopp/sosemanuk.cpp:356:3: error: Unexpected token!
                ".intel_syntax noprefix;"
                ^
<inline asm>:1:40: note: instantiated into assembly here
        .intel_syntax noprefix;mov QWORD PTR [%r11+1*8], rdi;mov QWORD PTR [...
                                              ^
embeddedcryptopp/sosemanuk.cpp:356:3: error: unexpected token in argument list
                ".intel_syntax noprefix;"
                ^
[...]

# patch-299a99e fixes the following error
$ make
[...]
clang -DNDEBUG -O2 -pipe -fPIC -DCRYPTOPP_DISABLE_ASM=1 -I. -I/usr/local/include/python2.7 -c embeddedcryptopp/cryptlib.cpp -o temp.freebsd-10-amd64-2.7/embeddedcryptopp/cryptlib.o -w
embeddedcryptopp/cryptlib.cpp:33:26: error: default initialization of an object of
      const type 'const CryptoPP::NullNameValuePairs' requires a user-provided
      default constructor
const NullNameValuePairs g_nullNameValuePairs;
                         ^
1 error generated.
error: command 'cc' failed with exit status 1
*** Error code 1