OS X fixes

These commits allow compiling HHVM on OS X 10.9 with its native clang compiler.

This also requires https://github.com/facebook/hhvm/pull/3159, https://github.com/facebook/folly/issues/75 and https://github.com/hhvm/hhvm-third-party/issues/18.

CMake config:
```bash
cmake .. \
    -DLIBIBERTY_LIB=$(brew --prefix binutilsfb)/lib/x86_64/libiberty.a \
    -DLIBEVENT_LIB=$(brew --prefix libevent)/lib/libevent.dylib \
    -DLIBEVENT_INCLUDE_DIR=$(brew --prefix libevent)/include \
    -DICU_INCLUDE_DIR=$(brew --prefix icu4c)/include \
    -DICU_LIBRARY=$(brew --prefix icu4c)/lib/libicuuc.dylib \
    -DICU_I18N_LIBRARY=$(brew --prefix icu4c)/lib/libicui18n.dylib \
    -DICU_DATA_LIBRARY=$(brew --prefix icu4c)/lib/libicudata.dylib \
    -DREADLINE_INCLUDE_DIR=$(brew --prefix readline)/include \
    -DREADLINE_LIBRARY=$(brew --prefix readline)/lib/libreadline.dylib \
    -DCURL_INCLUDE_DIR=$(brew --prefix curl)/include \
    -DCURL_LIBRARY=$(brew --prefix curl)/lib/libcurl.dylib \
    -DBOOST_INCLUDEDIR=$(brew --prefix boost)/include \
    -DBOOST_LIBRARYDIR=$(brew --prefix boost)/lib \
    -DBoost_USE_STATIC_LIBS=ON \
    -DJEMALLOC_INCLUDE_DIR=$(brew --prefix jemallocfb)/include \
    -DJEMALLOC_LIB=$(brew --prefix jemallocfb)/lib/libjemalloc.dylib \
    -DLIBINTL_LIBRARIES=$(brew --prefix gettext)/lib/libintl.dylib \
    -DLIBINTL_INCLUDE_DIR=$(brew --prefix gettext)/include \
    -DLIBDWARF_LIBRARIES=$(brew --prefix libdwarf)/lib/libdwarf.3.dylib \
    -DLIBDWARF_INCLUDE_DIRS=$(brew --prefix libdwarf)/include \
    -DLIBMAGICKWAND_INCLUDE_DIRS=$(brew --prefix imagemagick)/include/ImageMagick-6 \
    -DLIBMAGICKWAND_LIBRARIES=$(brew --prefix imagemagick)/lib/libMagickWand-6.Q16.dylib \
    -DMYSQL_INCLUDE_DIR=$(brew --prefix mysql)/include/mysql \
    -DMYSQL_LIB=$(brew --prefix mysql)/lib \
    -DFREETYPE_INCLUDE_DIRS=$(brew --prefix freetype)/include/freetype2 \
    -DFREETYPE_LIBRARIES=$(brew --prefix freetype)/lib/libfreetype.dylib \
    -DLIBSQLITE3_INCLUDE_DIR=$(brew --prefix sqlite)/include \
    -DLIBSQLITE3_LIBRARY=$(brew --prefix sqlite)/lib/libsqlite3.dylib
```