into class PackLinuxElf32x86 : public PackLinuxElf32Le : public PackLinuxElf32
which makes the code for compressing ELF (for direct-to-memory decompression)
cleaner because ELF has some of the class tree to itself.
This assumes PROT_EXEC|PROT_WRITE ought to work.
This is checked at runtime, and if it fails then
give a message on stderr and exit(127).
Modify --force-execve so that runtime avoids PROT_EXEC|PROT_WRITE.
Then executables compressed with --force-execve will run under
PaX, grSecurity, and strict SELinux.
