pkg/jerryscript: allow build with non-gnu toolchain, i.e. llvm

pkg/jerryscript/Makefile.jerryscript

@@ -13,16 +13,16 @@ JERRYHEAP  ?= 16
 libjerry:
 	mkdir -p $(BUILD_DIR)
 	cmake -B$(BUILD_DIR) -H./ \
+	 -DCMAKE_SYSTEM_NAME=RIOT \
+	 -DCMAKE_SYSTEM_PROCESSOR="$(MCPU)" \
+	 -DCMAKE_C_COMPILER=$(CC) \
+	 -DCMAKE_C_COMPILER_WORKS=TRUE \
 	 -DENABLE_LTO=OFF \
 	 -DFEATURE_VALGRIND=OFF \
-	 -DCMAKE_TOOLCHAIN_FILE=cmake/toolchain_external.cmake \
-	 -DJERRY_LIBC=OFF \
-	 -DJERRY_CMDLINE=OFF \
-	 -DJERRY_LIBM=OFF \
 	 -DENABLE_ALL_IN_ONE=OFF \
-	 -DEXTERNAL_CMAKE_SYSTEM_PROCESSOR="$(MCPU)" \
-	 -DEXTERNAL_CMAKE_C_COMPILER=$(CC) \
-	 -DEXTERNAL_CMAKE_C_COMPILER_ID=GNU \
+	 -DJERRY_LIBC=OFF \
+	 -DJERRY_LIBM=OFF \
+	 -DJERRY_CMDLINE=OFF \
 	 -DEXTERNAL_COMPILE_FLAGS="$(EXT_CFLAGS)" \
 	 -DMEM_HEAP_SIZE_KB=$(JERRYHEAP)