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/bl1/bl1.mk b/bl1/bl1.mk
index 53946ab..d118317 100644
--- a/bl1/bl1.mk
+++ b/bl1/bl1.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
 #
@@ -29,9 +29,9 @@
 BL1_SOURCES		+=	lib/pmf/pmf_main.c
 endif
 
-ifneq ($(findstring gcc,$(notdir $(LD))),)
+ifneq ($(findstring gcc,$(notdir $($(ARCH)-ld))),)
         BL1_LDFLAGS	+=	-Wl,--sort-section=alignment
-else ifneq ($(findstring ld,$(notdir $(LD))),)
+else ifneq ($(findstring ld,$(notdir $($(ARCH)-ld))),)
         BL1_LDFLAGS	+=	--sort-section=alignment
 endif