also support (and restrict to subsets) older chinese sets, and
explicitly refuse to convert to cjk (since there's no code for it yet)

these are useless legacy functions but some old software contains
cruft that expects them to exist...

this broke most uses of iconv in real-world programs, especially
glib's iconv wrappers.

STREAMS are utterly useless as far as I can tell, but some software
was apparently broken by the presence of stropts.h but lack of macros
it's supposed to define...

this should not be necessary - the invalid bit patterns cannot be
created except through type punning. however, some broken gnu software
is passing them to printf and triggering dangerous stack-smashing, so
let's catch them anyway...

hopefully this resolves the rest of the issues with hideously
nonportable hacks in programs that use gnulib.

this is a really ugly and backwards function, but its presence will
prevent lots of broken gnulib software from trying to define its own
version of fpurge and thereby failing to build or worse.

these interfaces are required to be thread-safe even though they are
not state-free. the random number sequence is shared across all
threads.

per POSIX: The mprotect() function shall change the access protections
to be that specified by prot for those whole pages containing any part
of the address space of the process starting at address addr and
continuing for len bytes.

on the other hand, linux mprotect fails with EINVAL if the base
address and/or length is not page-aligned, so we have to align them
before making the syscall.

this is mostly useless for shared libs (though it could help for
prelink-like purposes); the intended use case is for adding support
for calling the dynamic linker directly to run a program, as in:
./libc.so ./a.out foo

this usage is not yet supported.

prior to this change, copy relocations for initialized pointer
variables would not reflect the relocated contents of the pointer.

some cruft was left and DESTDIR was not being used correctly.

the path for the dynamic linker is now configurable, and failure to
install the symlink for it will not stop the build.

deps can be null if a library has no dependencies (such as libc itself)

basically we temporarily make the library and all its dependencies
part of the global namespace but only for the duration of performing
relocations, then return them to their former state.