tools/nolibc: Make dup2() rely on dup3() when available

tools/nolibc: Make dup2() rely on dup3() when available

A recent boot failure on 5.4-rc3 on arm64 revealed that sys_dup2()
is not available and that only sys_dup3() is implemented.  This commit
detects this and falls back to sys_dup3() when available.  This is a
port of nolibc's upstream commit fd5272ec2c66 to the Linux kernel.

Tested-by: Valentin Schneider <valentin.schneider@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com> [arm64]
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>