### Patch 1: Input Validation
To fix the CWE-787 vulnerability, we need to ensure that the input indices are within the bounds of the `b64` array. We can add a check before accessing the `b64` array elements.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    if (B64_BLOCK < 4) {
        // Handle error or return
        return;
    }
    ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
    ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
    ascii[2] = (uint8_t) (b64[2] << 6) | (b64[3]);
}
```

### Patch 2: Bounds Checking
We can add bounds checking to ensure that the `b64` array indices are within the valid range.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    if (B64_BLOCK >= 4) {
        ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
        ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
        ascii[2] = (uint8_t) (b64[2] << 6) | (b64[3]);
    } else {
        // Handle error or return
    }
}
```

### Patch 3: Array Index Validation
We can validate the array indices before accessing the `b64` array elements.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    if (b64[0] < 0 || b64[0] >= 256 || b64[1] < 0 || b64[1] >= 256 ||
        b64[2] < 0 || b64[2] >= 256 || b64[3] < 0 || b64[3] >= 256) {
        // Handle error or return
    } else {
        ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
        ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
        ascii[2] = (uint8_t) (b64[2] << 6) | (b64[3]);
    }
}
```

### Patch 4: Using a Safer Function
We can use a safer function like `memcpy` to copy the `b64` array elements into the `ascii` array.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    uint8_t temp[4];
    memcpy(temp, b64, 4);
    ascii[0] = (uint8_t) (temp[0] << 2) | (temp[1] >> 4);
    ascii[1] = (uint8_t) (temp[1] << 4) | (temp[2] >> 2);
    ascii[2] = (uint8_t) (temp[2] << 6) | (temp[3]);
}
```

### Patch 5: Error Handling
We can add error handling to catch any potential errors that may occur during the decoding process.

```c
static inline void DecodeBase64Block(uint8_t ascii[ASCII_BLOCK], uint8_t b64[B64_BLOCK])
{
    try {
        ascii[0] = (uint8_t) (b64[0] << 2) | (b64[1] >> 4);
        ascii[1] = (uint8_t) (b64[1] << 4) | (b64[2] >> 2);
        ascii[2] = (uint8_t) (b64[2] << 6) | (b64[3]);
    } catch (const std::exception& e) {
        // Handle error
    }
}
```

Note: The above patches are just examples and may need to be modified to fit the specific requirements of the code. Additionally, the `try-catch` block in Patch 5 is not applicable in C and is only used for demonstration purposes. In C, error handling is typically done using error codes or other mechanisms.