tccgen.c: Allow type attributes to prefix enum/struct/union name

From gcc docs: "You may also specify attributes between the enum, struct or union tag and the name of the type rather than after the closing brace."

Adds `82_attribs_position.c` in `tests/tests2`

tests/tests2/82_attribs_position.c

@@ -0,0 +1,14 @@
+typedef unsigned short uint16_t;
+typedef unsigned char uint8_t;
+
+typedef union Unaligned16a {
+  uint16_t u;
+  uint8_t b[2];
+} __attribute__((packed)) Unaligned16a;
+
+typedef union __attribute__((packed)) Unaligned16b {
+  uint16_t u;
+  uint8_t b[2];
+} Unaligned16b;
+
+int main () { return 0; }