Use shared libraries when building on Travis

[navsan]

[Identical to #21, but that got messed up due to some git foo.]

This change should reduce memory consumption and build time.
Comparing Travis run times for PR #21 (https://travis-ci.org/apache/incubator-quickstep/builds/136474629) with one from earlier today (https://travis-ci.org/apache/incubator-quickstep/builds/136370961), almost all the run times have gone down to a certain extent. It's particularly helpful for the GCC runs with copy elision (>10% speedup).

[pateljm]

LGTM. Merging.

[hbdeshmukh]

Hi @navsan

Have you tried compiling it with tcmalloc enabled? I am getting an error:

/usr/bin/ld: ../third_party/gperftools/lib/libtcmalloc_minimal.a(libtcmalloc_minimal_la-tcmalloc.o): relocation R_X86_64_32S against `.bss' can not be used when making a shared object; recompile with -fPIC
../third_party/gperftools/lib/libtcmalloc_minimal.a: could not read symbols: Bad value
clang-3.7: error: linker command failed with exit code 1 (use -v to see invocation)

This is clang 3.7 debug build on the CSL machine.

Edit: More details on the error.

[navsan]

Spoke to @hbdeshmukh offline. I don't currently have tcmalloc working on either of my dev boxes, so I'll debug this with his help by tomorrow.
Note that this is currently affecting builds with USE_TCMALLOC=On (default) and BUILD_SHARED_LIBS=On (non-default).