Add `-Wconversion` in CMakeLists.txt (#712)

Also fix warnings generated by this flag.

Signed-off-by: Gaurav Aggarwal <aggarg@amazon.com>

CMakeLists.txt

@@ -260,6 +260,7 @@ target_compile_options(freertos_kernel PRIVATE
     $<$<COMPILE_LANG_AND_ID:C,Clang,GNU>:-Wextra>
     $<$<COMPILE_LANG_AND_ID:C,Clang,GNU>:-Wpedantic>
     $<$<COMPILE_LANG_AND_ID:C,Clang,GNU>:-Werror>
+    $<$<COMPILE_LANG_AND_ID:C,Clang,GNU>:-Wconversion>
     $<$<COMPILE_LANG_AND_ID:C,Clang>:-Weverything>
 
     # Suppressions required to build clean with clang.

portable/MemMang/heap_4.c

@@ -421,7 +421,7 @@ static void prvHeapInit( void ) /* PRIVILEGED_FUNCTION */
     /* pxEnd is used to mark the end of the list of free blocks and is inserted
      * at the end of the heap space. */
     uxAddress = ( portPOINTER_SIZE_TYPE ) ( pucAlignedHeap + xTotalHeapSize );
-    uxAddress -= xHeapStructSize;
+    uxAddress -= ( portPOINTER_SIZE_TYPE ) xHeapStructSize;
     uxAddress &= ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK );
     pxEnd = ( BlockLink_t * ) uxAddress;
     pxEnd->xBlockSize = 0;

portable/MemMang/heap_5.c

@@ -508,7 +508,7 @@ void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions )
             configASSERT( pxEnd != NULL );
 
             /* Check blocks are passed in with increasing start addresses. */
-            configASSERT( xAddress > ( size_t ) pxEnd );
+            configASSERT( ( size_t ) xAddress > ( size_t ) pxEnd );
         }
 
         /* Remember the location of the end marker in the previous region, if
@@ -517,9 +517,9 @@ void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions )
 
         /* pxEnd is used to mark the end of the list of free blocks and is
          * inserted at the end of the region space. */
-        xAddress = xAlignedHeap + xTotalRegionSize;
+        xAddress = xAlignedHeap + ( portPOINTER_SIZE_TYPE ) xTotalRegionSize;
-        xAddress -= xHeapStructSize;
+        xAddress -= ( portPOINTER_SIZE_TYPE ) xHeapStructSize;
-        xAddress &= ~( ( size_t ) portBYTE_ALIGNMENT_MASK );
+        xAddress &= ~( ( portPOINTER_SIZE_TYPE ) portBYTE_ALIGNMENT_MASK );
         pxEnd = ( BlockLink_t * ) xAddress;
         pxEnd->xBlockSize = 0;
         pxEnd->pxNextFreeBlock = NULL;