rust: fix musl build

[ci skip]

srcpkgs/rust/patches/musl-dont-use-crt-static.patch

@@ -0,0 +1,11 @@
+Reason: https://gist.github.com/ab75b3796a9383423deecc0828494ac5
+--- rustc-1.28.0-src/src/librustc_target/spec/linux_musl_base.rs.orig   2018-10-08 21:02:21.588611506 +0200
++++ rustc-1.28.0-src/src/librustc_target/spec/linux_musl_base.rs        2018-10-08 21:02:40.846454873 +0200
+@@ -61,7 +61,7 @@
+     base.post_link_objects_crt.push("crtn.o".to_string());
+
+     // These targets statically link libc by default
+-    base.crt_static_default = true;
++    base.crt_static_default = false;
+     // These targets allow the user to choose between static and dynamic linking.
+     base.crt_static_respected = true;

srcpkgs/rust/template

@@ -89,10 +89,6 @@ esac
 post_extract() {
 	rm -rf src/llvm
 
-	case "$XBPS_MACHINE" in
-		*-musl) patch -p1 < $FILESDIR/musl.patch ;;
-	esac
-
 	if [ -z "$CROSS_BUILD" ]; then
 		mkdir -p stage0
 		cp -bflr ../rustc-*/rustc/* stage0
@@ -155,7 +151,7 @@ do_configure() {
 	fi
 	case "$XBPS_TARGET_MACHINE" in
 	*-musl)
-		configure_args+=" --musl-root=/usr"
+		configure_args+=" --set=target.${_host_triplet}.musl-root=/usr"
 		;;
 	esac