Frees a block of memory.
The memory must have been allocated via alloc or
alloc0 and the block_size has to match the size specified upon
allocation. Note that the exact release behaviour can be changed with the `G_DEBUG=gc-friendly` environment variable, also see
`G_SLICE` for related debugging options.
| block_size |
the size of the block |
| mem_block |
a pointer to the block to free |