MagnumExternal: Add ALC_SOFTX_HRTF defines and ALC_SOFT_HRTF procedures.

`ALC_SOFTX_HRTF` is the "in dev" hrtf extension present in OpenAL Soft
version 1.16.0, whereas `ALC_SOFT_HRTF` is the finished version of the Hrtf
extension, probably released with OpenAL Soft version 1.17.0.

Signed-off-by: Squareys <Squareys@googlemail.com>

src/MagnumExternal/OpenAL/extensions.h

@@ -26,6 +26,9 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <al.h>
+#include <alc.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -44,6 +47,12 @@ extern "C" {
 #define AL_FORMAT_STEREO_DOUBLE_EXT              0x10013
 #endif
 
+/* ALC_SOFTX_HRTF */
+#ifndef ALC_SOFTX_HRTF
+#define ALC_SOFTX_HRTF 1
+#define ALC_HRTF_SOFT                            0x1992
+#endif
+
 /* ALC_SOFT_HRTF */
 #ifndef ALC_SOFT_HRTF
 #define ALC_SOFT_HRTF 1
@@ -63,6 +72,9 @@ extern "C" {
 #define ALC_HRTF_REQUIRED_SOFT                   0x0003
 #define ALC_HRTF_HEADPHONES_DETECTED_SOFT        0x0004
 #define ALC_HRTF_UNSUPPORTED_FORMAT_SOFT         0x0005
+
+typedef ALCchar* (AL_APIENTRY*LPALGETSTRINGISOFT)(ALCdevice*,ALCenum,ALCsizei);
+typedef ALCboolean (AL_APIENTRY*LPALRESETDEVICESOFT)(ALCdevice*,const ALCint*);
 #endif
 
 #ifdef __cplusplus