fix npm install err on mips arch

[212dandan]

[loongson@localhost github]$ npm install ffi
|
> ffi@2.2.0 install /home/loongson/node_modules/ffi
> node-gyp rebuild

make: Entering directory '/home/loongson/node_modules/ffi/build'
  CC(target) Release/obj.target/ffi/deps/libffi/src/prep_cif.o
../deps/libffi/src/prep_cif.c:26:17: Fatal error: ffi.h: No such file or directory
  #include <ffi.h>
                  ^
Compile interrupt.
deps/libffi/ffi.target.mk:96: recipe for target 'Release/obj.target/ffi/deps/libffi/src/prep_cif.o' failed
make: *** [Release/obj.target/ffi/deps/libffi/src/prep_cif.o] Error 1
make: Leaving directory '/home/loongson/node_modules/ffi/build'
gyp ERR! build error 
gyp ERR! stack Error: `make` failed with exit code: 2
gyp ERR! stack     at ChildProcess.onExit (/usr/lib64/node_modules/npm/node_modules/node-gyp/lib/build.js:270:23)
gyp ERR! stack     at emitTwo (events.js:87:13)
gyp ERR! stack     at ChildProcess.emit (events.js:172:7)
gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:200:12)
gyp ERR! System Linux 3.10.84-17.fc21.loongson.mips64el
gyp ERR! command "/usr/bin/node" "/usr/lib64/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "rebuild"
gyp ERR! cwd /home/loongson/node_modules/ffi
gyp ERR! node -v v4.3.1
gyp ERR! node-gyp -v v3.0.3
gyp ERR! not ok 
npm ERR! Linux 3.10.84-17.fc21.loongson.mips64el
npm ERR! argv "/usr/bin/node" "/usr/bin/npm" "install" "ffi"
npm ERR! node v4.3.1
npm ERR! npm  v2.14.12
npm ERR! code ELIFECYCLE

npm ERR! ffi@2.2.0 install: `node-gyp rebuild`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the ffi@2.2.0 install script 'node-gyp rebuild'.
npm ERR! This is most likely a problem with the ffi package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     node-gyp rebuild
npm ERR! You can get their info via:
npm ERR!     npm owner ls ffi
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /home/loongson/github/npm-debug.log

I tested the Example in README.md passed, looks well:

[loongson@localhost node-ffi]$ node-gyp rebuild
gyp info it worked if it ends with ok
gyp info using node-gyp@0.10.6
gyp info using node@4.3.1 | linux | mips64el
(node) child_process: options.customFds option is deprecated. Use options.stdio instead.
gyp info spawn python
gyp info spawn args [ '/usr/bin/gyp',
gyp info spawn args   'binding.gyp',
gyp info spawn args   '-f',
gyp info spawn args   'make',
gyp info spawn args   '-I',
gyp info spawn args   '/home/loongson/github/node-ffi/build/config.gypi',
gyp info spawn args   '-I',
gyp info spawn args   '/usr/lib/node_modules/node-gyp/addon-rpm.gypi',
gyp info spawn args   '-I',
gyp info spawn args   '/usr/share/node/common.gypi',
gyp info spawn args   '-Dlibrary=shared_library',
gyp info spawn args   '-Dvisibility=default',
gyp info spawn args   '-Dnode_root_dir=/usr/share/node',
gyp info spawn args   '-Dmodule_root_dir=/home/loongson/github/node-ffi',
gyp info spawn args   '--depth=.',
gyp info spawn args   '--generator-output',
gyp info spawn args   'build',
gyp info spawn args   '-Goutput_dir=.' ]
gyp info spawn make
gyp info spawn args [ 'BUILDTYPE=Release', '-C', 'build' ]
make: Entering directory '/home/loongson/github/node-ffi/build'
  CC(target) Release/obj.target/ffi/deps/libffi/src/prep_cif.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/types.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/raw_api.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/java_raw_api.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/closures.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/mips/ffi.o
../deps/libffi/src/mips/ffi.c: In the function 'ffi_prep_args':
../deps/libffi/src/mips/ffi.c:84:13: Warning: Comparison Between Signed and Unsigned Integer Expressions [-Wsign-compare]
    if (bytes> 8 * sizeof (ffi_arg))
              ^
../deps/libffi/src/mips/ffi.c:107:47: Warning: Comparison Between Signed and Unsigned Integer Expressions [-Wsign-compare]
    for (i = 0, p_arg = ecif-> cif-> arg_types; i <ecif-> cif-> nargs; i ++, p_arg ++)
                                                ^
../deps/libffi/src/mips/ffi.c: In the function 'ffi_closure_mips_inner_O32':
../deps/libffi/src/mips/ffi.c:770:16: Warning: convert an integer to a pointer of a different size [-Wint-to-pointer-cast]
        rvalue = (void *) (UINT32) ar [0];
                 ^
../deps/libffi/src/mips/ffi.c: In the function 'ffi_closure_mips_inner_N32':
../deps/libffi/src/mips/ffi.c:946:45: Warning: convert a pointer to a different size integer [-Wpointer-to-int-cast]
           if ((arg_types[i]->type == FFI_TYPE_LONGDOUBLE) && ((unsigned)argp & (arg_types[i]->alignment-1)))
                                             ^
  CC(target) Release/obj.target/ffi/deps/libffi/src/mips/o32.o
  CC(target) Release/obj.target/ffi/deps/libffi/src/mips/n32.o
  AR(target) Release/obj.target/deps/libffi/libffi.a
  COPY Release/libffi.a
  CXX(target) Release/obj.target/ffi_bindings/src/ffi.o
  CXX(target) Release/obj.target/ffi_bindings/src/callback_info.o
  CXX(target) Release/obj.target/ffi_bindings/src/threaded_callback_invokation.o
  SOLINK_MODULE(target) Release/obj.target/ffi_bindings.node
  SOLINK_MODULE(target) Release/obj.target/ffi_bindings.node: Finished
  COPY Release/ffi_bindings.node
make: Leaving directory '/home/loongson/github/node-ffi/build'
gyp info ok