Fix toolchain selection logic and variable naming in build.mk

Author: G36maid

arch/riscv/build.mk

@@ -18,7 +18,7 @@ DEFINES := -DF_CPU=$(F_CLK) \
            -include config.h
 
 CROSS_COMPILE ?= riscv32-unknown-elf-
-CC     = $(CROSS_COMPILE)gcc
+C     = $(CROSS_COMPILE)gcc
 CC_IS_CLANG := $(shell $(CC) --version 2>/dev/null | grep -qi clang && echo 1)
 
 # Architecture flags
@@ -31,7 +31,7 @@ CFLAGS += $(ARCH_FLAGS)
 CFLAGS += -mstrict-align -ffreestanding -nostdlib -fomit-frame-pointer
 CFLAGS += $(INC_DIRS) $(DEFINES) -fdata-sections -ffunction-sections
 
-ifeq ($(TOOLCHAIN_TYPE),llvm)
+ifeq ($(CC_IS_CLANG),1)
     CC    = $(CROSS_COMPILE)clang
     AS    = $(CROSS_COMPILE)clang
     LD    = $(CROSS_COMPILE)ld.lld
@@ -46,7 +46,7 @@ ifeq ($(TOOLCHAIN_TYPE),llvm)
     ASFLAGS = --target=riscv32-unknown-elf $(ARCH_FLAGS)
     LDFLAGS = -m elf32lriscv --gc-sections
 else
-    CC    = $(CROSS_COMPILE)gcc
+    CC    = $(CC_DEFAULT)
     AS    = $(CROSS_COMPILE)as
     LD    = $(CROSS_COMPILE)ld
     DUMP  = $(CROSS_COMPILE)objdump -Mno-aliases