Move to /usr prefix.

- This is much more standard and replaces /image in sysa and is the
  standard in sysc (avoids many issues).
- GCC needs to have a file created for some unknown reason.
- Checksums updated.

sysc/zlib-1.2.11/checksums

@@ -0,0 +1 @@
+8e8255b1f90615cbb69f45697edcfd17dae492e090ca31c9d5390cb2d076e1b4  /image/lib/musl/libz.a

sysc/zlib-1.2.11/zlib-1.2.11.sh

@@ -0,0 +1,7 @@
+# SPDX-FileCopyrightText: 2021 Andrius Štikonas <andrius@stikonas.eu>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+src_configure() {
+    ./configure --prefix="${PREFIX}" --libdir="${PREFIX}/lib/musl" --static
+}