SIMD Everywhere finder needs to be installed alongside libobs CMake
package since its headers depends on it.
C++ cmath header is included on Windows on ARM to ensure that all math
functions are correctly defined when included in C++ code.
https://github.com/simd-everywhere/simde/issues/1304
macOS intrinsics is included to make sure that no redefinition error
happens.
With the removal of all legacy code paths, obsconfig.h always exists and
the compile definition always gets set. As such, it's no longer
necessary to check for it.
As removing the definition itself could be seen as a breaking change,
this simply moves the definition to pc.in and cmake.in files for now to
preserve the value for plugins that might expect this to be set. We may
remove the definition entirely in a later release.
tytan652