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/tools/encrypt_fw/Makefile b/tools/encrypt_fw/Makefile
index b530cca..83f2f57 100644
--- a/tools/encrypt_fw/Makefile
+++ b/tools/encrypt_fw/Makefile
@@ -63,8 +63,6 @@
 LIB_DIR := -L ${OPENSSL_DIR}/lib -L ${OPENSSL_DIR}
 LIB := -lssl -lcrypto
 
-HOSTCC ?= gcc
-
 .PHONY: all clean realclean --openssl
 
 all: --openssl ${BINARY}
@@ -72,12 +70,12 @@
 ${BINARY}: ${OBJECTS} Makefile
 	@echo "  HOSTLD  $@"
 	@echo 'const char build_msg[] = "Built : "__TIME__", "__DATE__;' | \
-                ${HOSTCC} -c ${HOSTCCFLAGS} -xc - -o src/build_msg.o
-	${Q}${HOSTCC} src/build_msg.o ${OBJECTS} ${LIB_DIR} ${LIB} -o $@
+                $(host-cc) -c ${HOSTCCFLAGS} -xc - -o src/build_msg.o
+	${Q}$(host-cc) src/build_msg.o ${OBJECTS} ${LIB_DIR} ${LIB} -o $@
 
 %.o: %.c
 	@echo "  HOSTCC  $<"
-	${Q}${HOSTCC} -c ${HOSTCCFLAGS} ${INC_DIR} $< -o $@
+	${Q}$(host-cc) -c ${HOSTCCFLAGS} ${INC_DIR} $< -o $@
 
 --openssl:
 ifeq ($(DEBUG),1)