Newer versions of MSVC are unhappy with the strategy of the build
environment redefining "inline" (even though they don't support the
actual keyword). Instead we define OPUS_INLINE to the right thing
in opus_defines.h.
This is the same approach we use for restrict.
There's no CPU detection for it, it only gets enabled by __SSE__
which gcc (other compilers?) defines automatically when supported
by -march=, which means at least all x86-64. For ia32, the user needs to
enable it in the CFLAGS.
