module_read_os_data() might not work

It looks for the program headers at `base + elf_hdr->e_phoff,` but `e_phoff` is the "program header table *file* offset", which is not in general the same as the offset in memory. I don't think it's possible to find the program headers from a pointer to the ELF file header in memory so the API of this function should be changed.

I noticed this because about 20 tests failed on an AArch64 system where the output from `readelf -l .../libstdc++.so.6` looked like this:
```
...
There are 8 program headers, starting at offset 12451840

Program Headers:
Type Offset VirtAddr PhysAddr
FileSiz MemSiz Flags Align
LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000
0x000000000018323b 0x000000000018323b R E 0x10000
...
LOAD 0x0000000000be0000 0x00000000001b0000 0x00000000001b0000
0x00000000000417a8 0x00000000000417a8 RW 0x10000
...
```
So the program headers are in that last loadable segment, which has file offset 0xbe0000 (= 12451840), but an offset in memory of 0x1b0000.

Unfortunately I'm not sure exactly where this `libstdc++.so.6` came from so I can't say how likely it is that this problem will affect other people.

Usually the program headers are in the same loadable segment as the ELF header, but I'm not sure that the ELF standards require the program headers to be loaded at all. If DynamoRIO is assuming something that is not required by the ELF standards then it would be good to document those assumptions.