* Don't build universal binaries by default
Starting Xcode 10 beta, there's no support for i386.
This commit changes the default build on iOS to regular libraries
instead of universal binaries.
Build of universal binaries is still supported with macos-universal.
* Add macos-no-universal option (compatibility)
Keep the default to be macos-no-universal, but add it as an option as
well for backward compatibility.
When compiling on linux, use GNUInstallDirs to automatically determine
the appropriate libdir path for multi-arch builds instead of hardcoding
lib/ or lib64/. GNUInstallDirs should follow the FHS appropriately for
non-debian platforms that place libs in lib64/. This also removes the
need to specify `lib64` on the command line when building for a
non-debian system that follows the linux FHS.
When compiling with cmake directly on debian and specifying
`-DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_LIBRARY_ARCHITECTURE=<arch>`, the
libdir should be set to /usr/lib/<arch>/.
bsharet