per the rules for hexadecimal integer constants, the previous
definitions were correctly treated as having unsigned type except
possibly when used in preprocessor conditionals, where all artithmetic
takes place as intmax_t or uintmax_t. the explicit 'u' suffix ensures
that they are treated as unsigned in all contexts.

since wint_t is unsigned, WINT_MIN needs to expand to an unsigned zero.

aside from the obvious C++ ABI purpose for this change, it also brings
musl into alignment with the compiler's idea of the definition of
wint_t (use in -Wformat), and makes the situation less awkward on ARM,
where wchar_t is unsigned.
internal code using wint_t and WEOF was checked against this change,
and while a few cases of storing WEOF into wchar_t were found, they
all seem to operate properly with the natural conversion from unsigned
to signed.

the arch-specific bits/alltypes.h.sh has been replaced with a generic
alltypes.h.in and minimal arch-specific bits/alltypes.h.in.
this commit is intended to have no functional changes except:
- exposing additional symbols that POSIX allows but does not require
- changing the C++ name mangling for some types
- fixing the signedness of blksize_t on powerpc (POSIX requires signed)
- fixing the limit macros for sig_atomic_t on x86_64
- making dev_t an unsigned type (ABI matching goal, and more logical)
in addition, some types that were wrongly defined with long on 32-bit
archs were changed to int, and vice versa; this change is
non-functional except for the possibility of making pointer types
mismatch, and only affects programs that were using them incorrectly,
and only at build-time, not runtime.
the following changes were made in the interest of moving
non-arch-specific types out of the alltypes system and into the
headers they're associated with, and also will tend to improve
application compatibility:
- netdb.h now includes netinet/in.h (for socklen_t and uint32_t)
- netinet/in.h now includes sys/socket.h and inttypes.h
- sys/resource.h now includes sys/time.h (for struct timeval)
- sys/wait.h now includes signal.h (for siginfo_t)
- langinfo.h now includes nl_types.h (for nl_item)
for the types in stdint.h:
- types which are of no interest to other headers were moved out of
 the alltypes system.
- fast types for 8- and 64-bit are hard-coded (at least for now); only
 the 16- and 32-bit ones have reason to vary by arch.
and the following types have been changed for C++ ABI purposes;
- mbstate_t now has a struct tag, __mbstate_t
- FILE's struct tag has been changed to _IO_FILE
- DIR's struct tag has been changed to __dirstream
- locale_t's struct tag has been changed to __locale_struct
- pthread_t is defined as unsigned long in C++ mode only
- fpos_t now has a struct tag, _G_fpos64_t
- fsid_t's struct tag has been changed to __fsid_t
- idtype_t has been made an enum type (also required by POSIX)
- nl_catd has been changed from long to void *
- siginfo_t's struct tag has been removed
- sigset_t's has been given a struct tag, __sigset_t
- stack_t has been given a struct tag, sigaltstack
- suseconds_t has been changed to long on 32-bit archs
- [u]intptr_t have been changed from long to int rank on 32-bit archs
- dev_t has been made unsigned
summary of tests that have been performed against these changes:
- nsz's libc-test (diff -u before and after)
- C++ ABI check symbol dump (diff -u before, after, glibc)
- grepped for __NEED, made sure types needed are still in alltypes
- built gcc 3.4.6

C++11, the first C++ with stdint.h, requires the previously protected
macros to be exposed unconditionally by stdint.h. apparently these
checks were an early attempt by the C committee to guess what the C++
committee would want, and they guessed wrong.

the preprocessor can reliably determine the signedness of wchar_t.
L'0円' is used for 0 in the expressions so that, if the underlying type
of wchar_t is long rather than int, the promoted type of the
expression will match the type of wchar_t.

the types of these expressions must match the integer promotions.
unsigned 8- and 16-bit values promote to signed int, not unsigned int.

per 7.18.4: Each invocation of one of these macros shall expand to an
integer constant expression suitable for use in #if preprocessing
directives. The type of the expression shall have the same type as
would an expression of the corresponding type converted according to
the integer promotions. The value of the expression shall be that of
the argument.
the key phrase is "converted according to the integer promotions".
thus there is no intent or allowance that the expression have
smaller-than-int types.

...and still be valid in #if directives.