depends: Make default host and build comparable

To detect cross-compiling, the host and build platforms are compared.
The `build` variable is always an output of `config.sub`, but the `host`
is not. This can lead to false results. For example, on OpenBSD:
 - host=amd64-unknown-openbsd7.5
 - build=x86_64-unknown-openbsd7.5

This change sets the default value of the `host` variable to the value
of `build`, ensuring cross-compiling won't be triggered when the `HOST`
variable is not set.

depends/Makefile

@@ -52,7 +52,6 @@ C_STANDARD ?= c11
 CXX_STANDARD ?= c++20
 
 BUILD = $(shell ./config.guess)
-HOST ?= $(BUILD)
 PATCHES_PATH = $(BASEDIR)/patches
 BASEDIR = $(CURDIR)
 HASH_LENGTH:=11
@@ -61,11 +60,6 @@ DOWNLOAD_RETRIES:=3
 HOST_ID_SALT ?= salt
 BUILD_ID_SALT ?= salt
 
-host:=$(BUILD)
-ifneq ($(HOST),)
-host:=$(HOST)
-endif
-
 ifneq ($(DEBUG),)
 release_type=debug
 else
@@ -75,9 +69,15 @@ endif
 base_build_dir=$(WORK_PATH)/build
 base_staging_dir=$(WORK_PATH)/staging
 base_download_dir=$(WORK_PATH)/download
-canonical_host:=$(shell ./config.sub $(HOST))
 build:=$(shell ./config.sub $(BUILD))
 
+host:=$(build)
+ifneq ($(HOST),)
+host:=$(HOST)
+endif
+HOST ?= $(BUILD)
+canonical_host:=$(shell ./config.sub $(HOST))
+
 build_arch =$(firstword $(subst -, ,$(build)))
 build_vendor=$(word 2,$(subst -, ,$(build)))
 full_build_os:=$(subst $(build_arch)-$(build_vendor)-,,$(build))