If the number of segments is greater than or equal to PN_XNUM (0xffff),
e_phnum is set to PN_XNUM, and the actual number of program header table
entries is contained in the sh_info field of the section header at index 0.
The phnum.m68k.so is a sample object file that tests this code path but then
actually only has 1 segment - it just indirects phnum through shdr0.
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