Allow building internal stubs for non-reentrant syscalls
if target provides its own malloc
* libc/reent/reent.c (errno): Move definition here.
* libc/reent/sbrkr.c: From here.
* libc/include/math.h (signgam): Change to errno-like solution
using a function to return the address of the real signgam.
* libc/reent/signgam.c: New file containing __signgam().
* libc/reent/Makefile.am: Added signgam.c to list of files.
* libc/reent/Makefile.in: Regenerated.
* libc/stdlib/mprec.c (ulp, b2d, d2b): changed a few expressions
like x << y-z to the equivalent x << (y-z).
(d2b): changed if statements with assignment to perform the
assignment prior to the if check.
* libc/reent/reent.c: included stdlib.h for "_free_r" prototype.
* libc/unix/getpass.c (getpass): moved "echo" assignment out of if.
* libc/unix/ttyname.c: included string.h for "strcpy" prototype.
* libc/unix/getcwd.c (ISDOT): added parentheses to clarify && and ||
precedence.
* libc/include/sys/unistd.h: added "vfork" prototype (for popen.c).
Added "_execve" prototype (for execl.c, execle.c, execv.c, and
execve.c).
* libc/posix/popen.c (popen): added parentheses to clarify && and ||
precedence.
* libm/math/e_cosh.c (__ieee754_cosh): changed parentheses to
clarify && and || precendence (and to remove pascalism).
* libm/math/e_sinh.c (__ieee754_sinh): Ditto.
* libm/math/s_infconst.c: added another pair of braces to all
initializers for __infinity (need three: for __infinity[1] array,
for union __dmath, and for i[2]).
* libc/stdlib/abort.c: changed description: uses "raise" instead of
"getpid" and "kill"; added: uses "write" and "_exit".
Also included unistd.h for "_exit" prototype.
* libc/stdlib/system.c: included unistd.h for "execve" prototype,
reent.h for "_fork_r" and "_wait_r" prototypes.
(do_system): changed extern char *environ[] to POSIX-friendly
extern char **environ.
* libc/stdlib/wctomb_r.c: included string.h for "strlen" and "strcmp"
prototypes.
* libc/stdlib/remove.c: included reent.h for "_unlink_r" prototype.
* libc/reent/execr.c: included sys/wait.h for "wait" prototype.
* libc/reent/fstatr.c: included sys/stat.h for "fstat" prototype.
* libc/reent/openr.c: included fcntl.h for "open" prototype.
* libc/reent/signalr.c: included signal.h for "kill" prototype,
unistd.h for "getpid" prototype.
* libc/reent/statr.c: included sys/stat.h for "stat" prototype.
* libc/reent/timer.c: included sys/time.h for "gettimeofday" prototype.
* libc/unix/getut.c (utmpname): removed local, incorrect "strdup"
prototype. Also included stdlib.h for "abort", string.h for
"strdup" and "strncmp" prototypes.
* libc/unix/getlogin.c: included string.h for "strncmp", "memset", and
"strncpy", unistd.h for "read" and "close" prototypes.
* libc/posix/execvp.c: included string.h for "strchr", "strlen", and
"strcat" prototypes.