cmake: Fix building without libsamplerate library

On Fedora, the headers for 32-bit and 64-bit are shared.
When building a 32-bit library, CMake found the header (that was installed
for the 64-bit libsamplerate development package). Because no 32-bit libsamplerate
library was installed, linking failed. (SDL_LIBSAMPLERATE_DYNAMIC was set to FALSE
because CMake could not find a library)

include/build_config/SDL_build_config.h.cmake

@@ -226,7 +226,7 @@
 #cmakedefine HAVE_O_CLOEXEC 1
 
 #cmakedefine HAVE_LIBUDEV_H 1
-#cmakedefine HAVE_LIBSAMPLERATE_H 1
+#cmakedefine HAVE_LIBSAMPLERATE 1
 #cmakedefine HAVE_LIBDECOR_H  1
 
 #cmakedefine HAVE_D3D_H @HAVE_D3D_H@