Fix audio strings with -use_readwrite_const and -signed (#1324)

* Fix audio strings with -use_readwrite_const and -signed

* Add comments for audio flags in makefile

src/code/audio_external_data.c

@@ -0,0 +1,69 @@
+#include "ultra64.h"
+#include "global.h"
+
+// sSoundRequests ring buffer endpoints. read index <= write index, wrapping around mod 256.
+u8 gSoundRequestWriteIndex = 0;
+u8 gSoundRequestReadIndex = 0;
+
+/**
+ * Array of pointers to arrays of SoundBankEntry of sizes: 9, 12, 22, 20, 8, 3, 5
+ *
+ * 0 : Player Bank          size 9
+ * 1 : Item Bank            size 12
+ * 2 : Environment Bank     size 22
+ * 3 : Enemy Bank           size 20
+ * 4 : System Bank          size 8
+ * 5 : Ocarina Bank         size 3
+ * 6 : Voice Bank           size 5
+ */
+SoundBankEntry* gSoundBanks[7] = {
+    D_8016BAD0, D_8016BC80, D_8016BEC0, D_8016C2E0, D_8016C6A0, D_8016C820, D_8016C8B0,
+};
+
+u8 gSoundBankSizes[ARRAY_COUNT(gSoundBanks)] = {
+    ARRAY_COUNT(D_8016BAD0), ARRAY_COUNT(D_8016BC80), ARRAY_COUNT(D_8016BEC0), ARRAY_COUNT(D_8016C2E0),
+    ARRAY_COUNT(D_8016C6A0), ARRAY_COUNT(D_8016C820), ARRAY_COUNT(D_8016C8B0),
+};
+
+u8 gSfxChannelLayout = 0;
+
+u16 D_801333D0 = 0;
+
+// The center of the screen in projected coordinates.
+// Gives the impression that the sfx has no specific location
+Vec3f gSfxDefaultPos = { 0.0f, 0.0f, 0.0f };
+
+// Reused as either frequency or volume multiplicative scaling factor
+// Does not alter or change frequency or volume
+f32 gSfxDefaultFreqAndVolScale = 1.0f;
+
+s32 D_801333E4 = 0; // unused
+
+// Adds no reverb to the existing reverb
+s8 gSfxDefaultReverb = 0;
+
+s32 D_801333EC = 0; // unused
+
+u8 D_801333F0 = 0;
+
+u8 gAudioSfxSwapOff = 0;
+
+u8 D_801333F8 = 0;
+
+s32 D_801333FC = 0; // unused
+
+u8 gSeqCmdWrPos = 0;
+u8 gSeqCmdRdPos = 0;
+u8 D_80133408 = 0;
+u8 D_8013340C = 1;
+
+u8 gSoundModeList[] = {
+    SOUNDMODE_STEREO,
+    SOUNDMODE_HEADSET,
+    SOUNDMODE_SURROUND,
+    SOUNDMODE_MONO,
+};
+
+u8 gAudioSpecId = 0;
+
+u8 D_80133418 = 0;