Initial depends addition

Depends cross compiles project dependencies for linux, mac and windows and multiple architectures.
Depends is original work by Cory Fields and used in bitcoin and a wide range of bitcoin related projects.

contrib/depends/patches/qt/fix_qt_pkgconfig.patch

@@ -0,0 +1,11 @@
+--- old/qtbase/mkspecs/features/qt_module.prf
++++ new/qtbase/mkspecs/features/qt_module.prf
+@@ -245,7 +245,7 @@
+ load(qt_targets)
+ 
+ # this builds on top of qt_common
+-!internal_module:!lib_bundle:if(unix|mingw) {
++unix|mingw {
+     CONFIG += create_pc
+     QMAKE_PKGCONFIG_DESTDIR = pkgconfig
+     host_build: \