Fix cmake build on windows

[Segfault1602]

CMake build was broken on windows due to M_E being undeclared. Fix is to define _USE_MATH_DEFINES on windows when building the library.

[Alloyed]

found this, and one other thing on my attempt to build msvc. in ladder.cpp

__attribute__((optimize("unroll-loops"))) void
void LadderFilter::ProcessBlock(float* buf, size_t size)
{
    for(size_t i = 0; i < size; i++)
    {
        buf[i] = Process(buf[i]);
    }
}

attribute is gcc-specific, causes msvc to not compile, and will be ignored on clang. alternatives:

• put unroll-loops in a macro that is empty on non-gcc platforms
• take size as a template parameter to reliably unroll the loop at compile time, example: https://stackoverflow.com/q/67599943