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/plat/rpi/rpi3/platform.mk b/plat/rpi/rpi3/platform.mk
index 06393e4..3af177c 100644
--- a/plat/rpi/rpi3/platform.mk
+++ b/plat/rpi/rpi3/platform.mk
@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2013-2023, Arm Limited and Contributors. All rights reserved.
+# Copyright (c) 2013-2024, Arm Limited and Contributors. All rights reserved.
 #
 # SPDX-License-Identifier: BSD-3-Clause
 #
@@ -52,9 +52,9 @@
 				${LIBFDT_SRCS}
 
 # Tune compiler for Cortex-A53
-ifeq ($(notdir $(CC)),armclang)
+ifeq ($(notdir $($(ARCH)-cc)),armclang)
     TF_CFLAGS_aarch64	+=	-mcpu=cortex-a53
-else ifneq ($(findstring clang,$(notdir $(CC))),)
+else ifneq ($(findstring clang,$(notdir $($(ARCH)-cc))),)
     TF_CFLAGS_aarch64	+=	-mcpu=cortex-a53
 else
     TF_CFLAGS_aarch64	+=	-mtune=cortex-a53