libobs: Use static library for version string information

Switching to a static library that contains version information as
const char strings has multiple benefits:

* The version information provided externally via compiler definitions
  will fail compilation early if malformed
* An updated version string (which will happen with every commit) will
  not invalidate existing compilation units, because only the static
  library is affected by the change
* An update of the version change just requires a recompilation of the
  static library and a linker update
* An update of the version will _not_ infect the rest of the codebase
  (as it does currently, because everything includes obsconfig.h one
  way or another)
* Other modules which used the macro definition directly have been
  updated as much as possible to use the proper getter method from
  `libobs` instead (some Windows-specific modules use preprocessor
  string composition, the value has been added as a compiler definition
  directly in those cases)
* Because the impact of a version change due to a commit hash change
  is limited to the static library, ccache hit rates should be
  improved considerably

UI/window-basic-about.cpp

@@ -24,7 +24,7 @@ OBSAbout::OBSAbout(QWidget *parent) : QDialog(parent), ui(new Ui::OBSAbout)
 		bitness = " (64 bit)";
 
 #ifdef HAVE_OBSCONFIG_H
-	ver += OBS_VERSION;
+	ver += obs_get_version_string();
 #else
 	ver += LIBOBS_API_MAJOR_VER + "." + LIBOBS_API_MINOR_VER + "." +
 	       LIBOBS_API_PATCH_VER;