mescc: Support GNU Bash.
* include/errno.h (EACCES, ENOSPC, ESPIPE): New macro.
* include/linux/x86/syscall.h (SYS_setuid, SYS_geteuid, SYS_getegid,
SYS_setgid): New macro.
* include/linux/x86_64/syscall.h: Likewise.
* include/stdint.h (LLONG_MIN, LLONG_MAX, SIZE_MAX): New macro.
* include/sys/stat.h (S_ISUID, S_ISGID, S_IXGRP, S_IXOTH, S_IRGRP,
S_IROTH, S_IWGRP, S_IWOTH, S_IRWXG, S_IRWXO): New macro.
* include/termio.h: New file.
* include/unistd.h (_POSIX_VERSION): New macro.
* lib/linux/gnu.c (geteuid, getegid, setuid, setgid): New function.
* lib/string/memchr.c: New file.
* lib/stub/getpwuid.c: New file.
* lib/stub/rand.c: New file.
* lib/stub/ttyname.c: New file.
* include/string.h (memchr): Declare.
* include/unistd.h (geteuid, getegid, setuid, setgid): Declare.
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