#define ZMQ_HAVE_WINDOWS_TARGET_XP disable uncompatible WinAPI
1. Disable call if_indextoname()
2. Emulate windows Condition Variable API in class condition_variable_t with std::condition_variable
This code can be compiled in MSVC 2015 with option "Platform toolset: Visual Studio 2015 - Windows XP (v140_xp)"
Solution: Rename the custom implementation of clock_gettime for macOS to
alt_clock_gettime and wrap all usage in preprocessor macros to only enable the
alternative version when using macOS <= 10.11.
This issue occurs when targeting macOS 10.11 or earlier but using the 10.12
or newer SDK.
Solution: use the less nice but correct int constant 1000000000
instead of the shorter 1E9 to avoid a compiler warning when assigning
to timespec.tv_nsec, which is a long int.
Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.
Solution: specify these grants in the header of each source file.
