[Maintenance] [th04/th05] Declare BGM and SE modes in C land

Part of P0077, funded by Splashman and -Tom-.

th04/snd/detmodes.asm

@@ -1,8 +1,4 @@
-; Checks the requested BGM and SE modes against the available hardware and
-; sets snd_se_mode and snd_bgm_mode accordingly.
-; Returns snd_bgm_mode, but the game doesn't care.
-
-; int __pascal snd_determine_modes(int req_bgm_mode, int req_se_mode)
+public SND_DETERMINE_MODES
 snd_determine_modes	proc
 @@req_se_mode	= word ptr (cPtrSize + 2)
 @@req_bgm_mode	= word ptr (cPtrSize + 4)

th04/snd/snd.h

@@ -0,0 +1,23 @@
+#include "th02/snd/snd.h"
+
+typedef enum {
+	SND_BGM_OFF = 0,
+	SND_BGM_FM26 = 1,
+	SND_BGM_FM86 = 2,
+	SND_BGM_MODE_COUNT = 3,
+	SND_BGM_MIDI = 3, // unsupported
+} snd_bgm_mode_t;
+
+typedef enum {
+	SND_SE_OFF = 0,
+	SND_SE_FM = 1,
+	SND_SE_BEEP = 2,
+	SND_SE_MODE_COUNT = 3,
+} snd_se_mode_t;
+
+extern unsigned char snd_se_mode;
+extern unsigned char snd_bgm_mode;
+
+// Checks the requested BGM and SE modes against the available hardware and
+// sets [snd_se_mode] and [snd_bgm_mode] accordingly. Returns [snd_bgm_mode].
+unsigned char pascal snd_determine_modes(int req_bgm_mode, int req_se_mode);

th04/snd/snd[data].asm

@@ -1,11 +1,9 @@
-; enum BGM_MODE
 SND_BGM_OFF = 0
 SND_BGM_FM26 = 1
 SND_BGM_FM86 = 2
 SND_BGM_MODE_COUNT = 3
 SND_BGM_MIDI = 3 ; unsupported
 
-; enum SE_MODE
 SND_SE_OFF = 0
 SND_SE_FM = 1
 SND_SE_BEEP = 2