tools,gen-expr: generate intermediate files under /tmp

tools/gen-expr/Makefile

@@ -5,4 +5,4 @@ $(APP): gen-expr.c
 
 .PHONY: clean
 clean:
-	-rm $(APP) .code.c .expr 2> /dev/null
+	-rm $(APP) 2> /dev/null

tools/gen-expr/gen-expr.c

@@ -97,12 +97,15 @@ int main(int argc, char *argv[]) {
 
     sprintf(code_buf, code_format, buf);
 
-    FILE *fp = fopen(".code.c", "w");
+    FILE *fp = fopen("/tmp/.code.c", "w");
     assert(fp != NULL);
     fputs(code_buf, fp);
     fclose(fp);
 
-    fp = popen("gcc .code.c -Wall -Werror -o .expr && ./.expr", "r");
+    int ret = system("gcc /tmp/.code.c -o /tmp/.expr");
+    if (ret != 0) continue;
+
+    fp = popen("/tmp/.expr", "r");
     assert(fp != NULL);
     int result;
     fscanf(fp, "%d", &result);