depends: Force CMAKE_EXPORT_NO_PACKAGE_REGISTRY=TRUE

When using CMake policies 3.14 and below, the `export(PACKAGE)` command
by default populates the user package registry, which is stored outside
the build tree. Setting the `CMAKE_EXPORT_NO_PACKAGE_REGISTRY` variable
disables this side effect.

In CMake 3.15 and later, this behavior is disabled by default, and the
variable has no effect.

depends/funcs.mk

@@ -224,6 +224,7 @@ $(1)_cmake=env CC="$$($(1)_cc)" \
                -DCMAKE_INSTALL_LIBDIR=lib/ \
                -DCMAKE_POSITION_INDEPENDENT_CODE=ON \
                -DCMAKE_VERBOSE_MAKEFILE:BOOL=$(V) \
+               -DCMAKE_EXPORT_NO_PACKAGE_REGISTRY:BOOL=TRUE \
                $$($(1)_config_opts)
 ifeq ($($(1)_type),build)
 $(1)_cmake += -DCMAKE_INSTALL_RPATH:PATH="$$($($(1)_type)_prefix)/lib"