CDH-18418. Fixing invalid type conversions on some systems.

    Compilation of gperftools fails on some operating systems with a compiler
    error due to an invalid conversion from signinfo_t. gpertools issue #444
    fixes this by using siginfo instead, however on Ubuntu 14.04 this is also
    an invalid conversion, and int appears to be the only type that is a valid
    conversion across all support distros.

    See: https://code.google.com/p/gperftools/issues/detail?id=444

Change-Id: Ie71b4bb8babb4d0403b59973e2ddf5e32f10d12b
CDH-18415. Explicitly linking against crypto library

    Without specifying crypto in target_link_libraries, it is possible for the
    build to fail because it is unable to find the symbols from libcrypto.

Change-Id: Ib1eb921e7d2fa849eb623f9102911a7e42f87ed2
CDH-20407. Make it possible for Impala build to point at arbitrary locations for Boost libraries.

    Before, System directories were being included with higher precedence than other
    directories returned by find_* modules. Such modules should be checking in System
    locations anyway and the precedence should be honored (specifically with Boost, as many
    distros do not ship an appropriate version of Boost libraries). This also works around
    a bug in some CMake versions where System locations always take precedence over
    BOOST_ROOT, as documented here:

        http://www.cmake.org/pipermail/cmake/2011-November/047533.html

Change-Id: I5f658ce1121f99f4cd5f6e51944e2951c6cac544
CDH-18430. Snappy build fails for various reasons on various distros

    Using the build scripts shipped with the official Snappy release, the build
    can occasionally fail due to special characters in the path and race
    conditions, and these failures do not always occur consistently. This
    forces autotools to regenerate the build scripts each time and overwrite
    existing scripts, and works around several problems encountered when
    regenerating on older distros including doc_dir not having a default value
    and initializing libtool a different way.

Change-Id: I326a656d4c3c258e5eb71f69f54eee6b6d434290