libzip: use Requires.private rather than Requires

src/libzip-2-pkgconfig_private.patch

@@ -0,0 +1,16 @@
+This file is part of MXE.
+See index.html for further information.
+
+Only advertise -lz for static builds.
+
+--- a/libzip.pc.in	2012-03-15 10:28:05.000000000 +0100
++++ b/libzip.pc.in	2012-12-18 22:48:27.807773881 +0100
+@@ -9,6 +9,7 @@
+ Name: libzip
+ Description: library for handling zip archives
+ Version: @VERSION@
+-Libs: -L${libdir} -lzip @LIBS@
++Libs: -L${libdir} -lzip
+ Cflags: -I${includedir} -I${libincludedir}
++Requires.private: zlib
+ 

src/libzip.mk

@@ -16,9 +16,6 @@ define $(PKG)_UPDATE
 endef
 
 define $(PKG)_BUILD
-# TODO: send a patch upstream
-    echo 'Requires: zlib' >> '$(1)/libzip.pc.in'
-
     cd '$(1)' && ./configure \
         --host='$(TARGET)' \
         --prefix='$(PREFIX)/$(TARGET)' \