libmagicrt: integrate into build system

The magic runtime library is now built as part of the regular build, if
the MKMAGIC=yes flag is passed to the build system. The library has
been renamed from

libmagicrt: integrate into build system

The magic runtime library is now built as part of the regular build, if
the MKMAGIC=yes flag is passed to the build system. The library has
been renamed from "magic" to "magicrt" to resolve a name clash with BSD
file(1)'s libmagic. All its level-5 LLVM warnings have been resolved.
The final library, "libmagicrt.bcc", is now stored in the destination
library directory rather than in the source tree.

Change-Id: Iebd4b93a2cafbb59f95d938ad1edb8b4f6e729f6

show more ...