use ALFUNC() in i_pcsound.c, avoid code duplication

src/i_pcsound.c

@@ -21,6 +21,7 @@
 
 #include "doomstat.h"
 #include "doomtype.h"
+#include "i_oalcommon.h"
 #include "i_oalsound.h"
 #include "i_printf.h"
 #include "i_sound.h"
@@ -31,16 +32,6 @@
 #include "w_wad.h"
 #include "z_zone.h"
 
-// C doesn't allow casting between function and non-function pointer types, so
-// with C99 we need to use a union to reinterpret the pointer type. Pre-C99
-// still needs to use a normal cast and live with the warning (C++ is fine with
-// a regular reinterpret_cast).
-#if __STDC_VERSION__ >= 199901L
-#  define FUNCTION_CAST(T, ptr) (union{void *p; T f;}){ptr}.f
-#else
-#  define FUNCTION_CAST(T, ptr) (T)(ptr)
-#endif
-
 static LPALBUFFERCALLBACKSOFT alBufferCallbackSOFT;
 static ALuint callback_buffer;
 static ALuint callback_source;
@@ -288,8 +279,7 @@ static void RegisterCallback(void)
                  "RegisterCallback: AL_SOFT_callback_buffer not found.");
         return;
     }
-    alBufferCallbackSOFT = FUNCTION_CAST(
-        LPALBUFFERCALLBACKSOFT, alGetProcAddress("alBufferCallbackSOFT"));
+    ALFUNC(LPALBUFFERCALLBACKSOFT, alBufferCallbackSOFT);
 
     alGenBuffers(1, &callback_buffer);
     alGenSources(1, &callback_source);