build: use new toolchain variables for tools

This change migrates the values of `CC`, `CPP`, `AS` and other toolchain
variables to the new `$(toolchain)-$(tool)` variables, which were
introduced by the toolchain refactor patch. These variables should be
equivalent to the values that they're replacing.

Change-Id: I644fe4ce82ef1894bed129ddb4b6ab94fb04985d
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/make_helpers/windows.mk b/make_helpers/windows.mk
index 980abf0..7ed8e84 100644
--- a/make_helpers/windows.mk
+++ b/make_helpers/windows.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2016-2023, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2016-2024, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -88,8 +88,7 @@
 define MAKE_BUILD_STRINGS
 	$$(file >$1.in,$$(TF_CFLAGS) $$(CFLAGS))
 	@echo $$(BUILT_TIME_DATE_STRING) $$(VERSION_STRING_MESSAGE) $$(VERSION_MESSAGE) | \
-		$$(CC) @$1.in -x c -c - -o $1
+		$($(ARCH)-cc) @$1.in -x c -c - -o $1
 endef
 
 MSVC_NMAKE := nmake.exe
-