fix #1246 (#1254)

* fix finding python path which only has python3.

* fix #1246, arm host issue.

* skip assembler tests on non-x86 host.

* update macro of dummy value.

* fix MSVC macro.

* update dummy array value macro.

* restore to original qemu code.

tests/unit/unicorn_test.h

@@ -42,7 +42,14 @@ do {                                                                \
 char * read_file(const char *filename, struct stat *info) {
     stat(filename, info);
     char *code = malloc(info->st_size);
+    if (code == NULL) {
+        return NULL;
+    }
     FILE *fp = fopen(filename, "r");
+    if (fp == NULL) {
+        free(code);
+        return NULL;
+    }
     fread(code, info->st_size, 1, fp);
     return code;
 }