depends: Amend handling flags environment variables

If any of {C,CXX,CPP,LD}FLAGS is specified it should be assigned to
a non-type-specific variable.

depends/hosts/default.mk

@@ -28,8 +28,8 @@ endef
 
 define add_host_flags_func
 ifeq ($(filter $(origin $1),undefined default),)
-$(host_arch)_$(host_os)_$1 =
-$(host_arch)_$(host_os)_$(release_type)_$1 = $($1)
+$(host_arch)_$(host_os)_$1 = $($1)
+$(host_arch)_$(host_os)_$(release_type)_$1 =
 else
 $(host_arch)_$(host_os)_$1 += $($(host_os)_$1)
 $(host_arch)_$(host_os)_$(release_type)_$1 += $($(host_os)_$(release_type)_$1)