Fix compiler warnings with optimizations enabled

[tony-josi-aws]

Description

This PR fixes compiler warnings that are generated when compiled with optimizations enabled in GCC and adds CI build checks with optimization settings on.

Thanks, @StefanBalt, for reporting this issue in #1217.

This PR also fixes the false positive warnings emitted by GCC version GNU 13.1.0:

/home/ubuntu/Projects/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Callback.c: In function ‘xDNSDoCallback’:
/home/ubuntu/Projects/FreeRTOS-Plus-TCP/build/_deps/freertos_kernel-src/include/./list.h:241:75: error: array subscript ‘ListItem_t {aka const struct xLIST_ITEM}[0]’ is partly outside array bounds of ‘List_t[1]’ {aka ‘struct xLIST[1]’} [-Werror=array-bounds=]
  241 | #define listGET_NEXT( pxListItem )                        ( ( pxListItem )->pxNext )
      |                                                                           ^~
/home/ubuntu/Projects/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Callback.c:72:54: note: in expansion of macro ‘listGET_NEXT’
   72 |             for( pxIterator = ( const ListItem_t * ) listGET_NEXT( pxEnd );
      |                                                      ^~~~~~~~~~~~
/home/ubuntu/Projects/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Callback.c:45:19: note: at offset 16 into object ‘xCallbackList’ of size 40
   45 |     static List_t xCallbackList;

Test Steps

Tested with DNS

Checklist:

• I have tested my changes. No regression in existing tests.
• [ ] I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

#1217

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[archigup]

This will create warnings on compilers that always warn on strcpy.

Do we have Clang in CI?

If it doesnt warn on the compilers we we support, should be fine.

[StefanBalt]

This will create warnings on compilers that always warn on strcpy.

@archigup do you think memcpy() would be the better choice?

[tony-josi-aws]

@archigup @StefanBalt
Clang seems to be fine with strcpy: https://godbolt.org/z/7b5bW7f73