Add minimp3 include to CFLAGS, because reasons?

Honestly not sure why it have to be here and being on fmt is not enough.

Makefile

@@ -6,7 +6,7 @@ INSTALL_DIR ?= $(PREFIX)
 
 LIBS=fmt sdl ssl openal ui uv mysql
 
-CFLAGS = -Wall -O3 -I src -msse2 -mfpmath=sse -std=c11 -I include/pcre -I include/mikktspace -D LIBHL_EXPORTS
+CFLAGS = -Wall -O3 -I src -msse2 -mfpmath=sse -std=c11 -I include/pcre -I include/mikktspace -I include/minimp3 -D LIBHL_EXPORTS
 LFLAGS = -L. -lhl
 LIBFLAGS =
 HLFLAGS = -ldl