Add symlink from libc.so to libc.so.6

Typically it's the other way around, but we can't have shared library named libc.so.6 in target/release directory.
cargo includes 'target/release' in LD_LIBRARY_PATH for build script, so even if clean build runs fine,
every subsquent run will make build script link with relibc.

Makefile

@@ -86,6 +86,7 @@ install-libs: libs
 	mkdir -pv "$(DESTDIR)/lib"
 	cp -v "$(BUILD)/release/libc.a" "$(DESTDIR)/lib"
 	cp -v "$(BUILD)/release/libc.so" "$(DESTDIR)/lib"
+	ln -sr "$(DESTDIR)/lib/libc.so" "$(DESTDIR)/lib/libc.so.6"
 	cp -v "$(BUILD)/release/crt0.o" "$(DESTDIR)/lib"
 	cp -v "$(BUILD)/release/crti.o" "$(DESTDIR)/lib"
 	cp -v "$(BUILD)/release/crtn.o" "$(DESTDIR)/lib"