This patch moves getMultiarchPath() to Platform so that it is available for
both Library and NativeLibrary.

It also fixes the library path on the aarch64, armhf and ppc64el platforms.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1028374 for more info.

• Commit 4d3927c
• #1499: try to load library from /usr/lib/jni if property jna.boot.library.path is not set
• Branch master

niol