Add SIGABRT const to newlib

(apply <rust-lang#3658> to `main`)
(cherry picked from commit 47a8927)

Author: Tevz-Beskovnik

src/unix/newlib/mod.rs

@@ -508,6 +508,8 @@ pub const SOCK_CLOEXEC: ::c_int = O_CLOEXEC;
 
 pub const INET_ADDRSTRLEN: ::c_int = 16;
 
+pub const SIGABRT: ::c_int = 1;
+
 // https://github.com/bminor/newlib/blob/HEAD/newlib/libc/sys/linux/include/net/if.h#L121
 pub const IFF_UP: ::c_int = 0x1; // interface is up
 pub const IFF_BROADCAST: ::c_int = 0x2; // broadcast address valid