The floating-point build calls a number of math library
functions, and linking with libm is technically necessary.
It wasn't obvious because most systems support shlib
dependencies and pulled it in that way, or supply the
referenced functions with intrinsics. Discovered the issue
trying to build libopusfile against the uninstalled static
libopus, which unlike opus-tools, doesn't itself need libm.

The -lm argument is only added to Libs for the floating-
point (default) build. It's not necessary for the fixed-
point build.

Also mark which build was used in the .pc file description.

While a feature of Opus, its applications are not limited
to contexts where low delay is important.

Ralph Giles authored 13 years ago and Jean-Marc Valin committed 13 years ago

These files allow compiling and linking against the reference
implementation with an invocation like `pkg-config --cflags
--libs opus`. They're optional within the opus build system,
but can simplify compilation for clients and are generally
considered part of a normal autotools build these days.

The -uninstalled version refers to local build products
within the tree, which is helpful for testing and unprivileged
builds. opus.pc is used once 'make install' has put the
libraries and headers somewhere more permanent.