As MUSL libc does not provide netax25/ax25.h, netrom/netrom.h and 
netrose/rose.h instatll substitute files uncondiditionally. See bug #907465

diff --git a/Makefile.am b/Makefile.am
index 0ff5f37..517e084 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -7,15 +7,9 @@ libax25ioincludedir = $(includedir)
 AM_CPPFLAGS = -DAX25_SYSCONFDIR=\""$(sysconfdir)/ax25/"\" \
 	      -DAX25_LOCALSTATEDIR=\""$(localstatedir)/ax25/"\"
 
-if !AX25_H
 USE_LIBAX25_AX25_H = netax25/ax25.h
-endif
-if !NETROM_H
 USE_LIBAX25_NETROM_H = netrom/netrom.h
-endif
-if !ROSE_H
 USE_LIBAX25_ROSE_H = netrose/rose.h
-endif
 
 nobase_libax25include_HEADERS = 	\
 	netax25/axlib.h			\