update to musl 1.1.18 and make it the default

Makefile

@@ -4,7 +4,7 @@ SOURCES = sources
 CONFIG_SUB_REV = 3d5db9ebe860
 BINUTILS_VER = 2.27
 GCC_VER = 6.3.0
-MUSL_VER = 1.1.17
+MUSL_VER = 1.1.18
 GMP_VER = 6.1.1
 MPC_VER = 1.0.3
 MPFR_VER = 3.1.4

hashes/musl-1.1.18.tar.gz.sha1

@@ -0,0 +1 @@
+d4e2949afbcdd1d543703bc1728f01bff2f85560  musl-1.1.18.tar.gz