Use TARGET instead of PREFIX in /tests Makefile(s) (#1647)

tests/Makefile

@@ -2,14 +2,14 @@
 # RISCV Toolchain
 #################################
 
-PREFIX = riscv64-unknown-elf-
+TARGET = riscv64-unknown-elf
 
-GCC = $(PREFIX)gcc
-CXX = $(PREFIX)g++
-CP = $(PREFIX)objcopy
-OBJDUMP = $(PREFIX)objdump
-DG = $(PREFIX)gdb
-SIZE = $(PREFIX)size
+GCC = $(TARGET)-gcc
+CXX = $(TARGET)-g++
+CP = $(TARGET)-objcopy
+OBJDUMP = $(TARGET)-objdump
+DG = $(TARGET)-gdb
+SIZE = $(TARGET)-size
 
 
 #################################

tests/libgloss.mk

@@ -5,6 +5,10 @@ ifndef GCC
 $(error GCC is not defined)
 endif
 
+ifndef TARGET
+$(error TARGET is not defined)
+endif
+
 libgloss_specs := htif_nano.specs
 
 # Test whether libgloss-htif is globally installed and usable