Make ARM tests mimic m68k behaviour of signed char by default

This way we can use `s8` from the SGDK.

src/midi.c

@@ -933,7 +933,7 @@ void midi_tick(void)
             if (state->midiChannel == chan && state->noteOn) {
 
                 u8 pitch = state->pitch;
-                signed char cents = state->cents;
+                s8 cents = state->cents;
 
                 if (midiChannel->glideTargetPitch > pitch) {
                     cents += 10;
@@ -945,8 +945,8 @@ void midi_tick(void)
                     state->ops->pitch(state->number, pitch, cents);
                     state->pitch = pitch;
                     state->cents = cents;
-                } else if (midiChannel->glideTargetPitch < pitch || (midiChannel->glideTargetPitch
-                        == pitch && cents > 0)) {
+                } else if (midiChannel->glideTargetPitch < pitch
+                    || (midiChannel->glideTargetPitch == pitch && cents > 0)) {
                     cents -= 10;
                     if (cents == -10) {
                         pitch--;

src/midi.h

@@ -140,7 +140,7 @@ typedef struct DeviceChannel {
     u8 volume;
     u8 pan;
     u16 pitchBend;
-    signed char cents;
+    s8 cents;
 } DeviceChannel;
 
 void midi_init(const FmChannel** defaultPresets, const PercussionPreset** defaultPercussionPresets,

tests/Makefile

@@ -32,7 +32,8 @@ CFLAGS=$(INCLUDE_DIRS) \
 	-Wno-char-subscripts \
 	-Wno-unused-parameter \
 	-Wno-builtin-declaration-mismatch \
-	-Wno-unused-function
+	-Wno-unused-function \
+	-fsigned-char
 
  # list of function signature to mock
 MOCKS=midi_process \