Reduce package size

[lgeiger]

This PR introduces two changes:

• Build libzmq with 2 cores only: I timed it here and it doesn't make sense to use more on a average machine.
• Remove libzmq source after build: This will reduce the package size by about 16.5 MB. I'm leaving the .tar.gz file so it doesn't have to be downloaded again on rebuilding (795KB).

/cc @rgbkrk @n-riesco

[codecov-io]

Current coverage is 91.16% (diff: 100%)

Merging #86 into master will not change coverage

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[rgbkrk]

This is helpful for electron and for when this is used in Docker or other container environments.

[n-riesco]

I've just tested this PR on a 32bit notebook. The notebook freezes no more and the compilation time has been reduced:

$ time node_module/.bin/prebuild --install
[...]

real    4m6.572s
user    6m28.968s
sys     0m32.784s

[lgeiger]

@n-riesco that's great!

Would we get even better times if we use make instead of make -j 2 on your system?

[n-riesco]

I get a longer time (but bear in mind that the proper way to do a comparison like this would require running both tests a number of times):

$ git diff
diff --git a/build_libzmq.sh b/build_libzmq.sh
index bde4101..0dc33dd 100755
--- a/build_libzmq.sh
+++ b/build_libzmq.sh
@@ -23,7 +23,7 @@ cd $ZMQ_SRC_DIR

 test -f configure || ./autogen.sh
 ./configure --prefix=$ZMQ_PREFIX --with-relaxed --enable-static --disable-shared
-make -j 2
+make
 make install

 cd $ZMQ_PREFIX


$ time node_modules/.bin/prebuild --install
[...]

real    7m6.190s
user    6m15.212s
sys 0m36.044s

[n-riesco]

This commit however is going to make my yarn times longer, because it'll delete all the object files from the cache.

[lgeiger]

@n-riesco Thanks for testing. This confirmed my guess that we hit the sweet spot with make -j 2.

This commit however is going to make my yarn times longer, because it'll delete all the object files from the cache.

That's kind of expected. But I prefer a smaller package size over a faster build considering that users likely won't rebuild zeromq very often.

@rgbkrk What do you think?

[rgbkrk]

A smaller package size certainly helps us in the Electron and Atom case.

An aside: At least on the nteract notebook, we can't use yarn until they support rebuilds (for electron).

What packages are you using yarn with? IJavaScript?

[n-riesco]

@rgbkrk I've only started using yarn so that I could test this package in my notebook.