Implement _strlwr for non-Windows platforms

_strlwr is not present on non-Windows platforms.

midi-utils.c

@@ -1,5 +1,15 @@
 #include "midi-utils.h"
 
+#if !defined __WIN32
+void _strlwr(char* dest) {
+	for (unsigned int i = 0; i < strlen(dest); i += 1) {
+		if ('A' <= dest[i] && dest[i] <= 'Z') {
+			dest[i] += 0x20;
+		}
+	}
+}
+#endif
+
 char* MIDI_GetNoteName(unsigned char midi_note) {
 	static const char* pitch_names[] = {
 		"C",