7zip reader: add support for POWERPC filter for non-LZMA compressors (#2459)

7zip reader: add support for POWERPC filter for non-LZMA compressors (#2459)

This new test archive contains a C hello world executable built like so
on a ubuntu 24.04 machine:
```
#include <stdio.h>

int main(int argc, char *argv[]) {
  printf("hello, world\n");
  return 0;
}
```

`powerpc-linux-gnu-gcc hw.c -o hw-powerpc -Wall`

The test archive that contains this executable was created like so,
using 7-Zip 24.08:
`7zz a -t7z -m0=deflate -mf=ppc
libarchive/test/test_read_format_7zip_deflate_powerpc.7z hw-powerpc`

This test fails in the first commit in this PR, and passes in the second
commit.