…channel to create and delete channels.

child_argv[argc+extra_args] is outside the allocated memory region,
since it starts counting from 0.

Seen with valgrind:

==22732== Invalid write of size 8
==22732==    at 0x5E876D4: exec_am_broadcast (termux-api.c:254)
==22732==  Address 0x6033e10 is 0 bytes after a block of size 144 alloc'd
==22732==    at 0x5CC9FB4: malloc (in /data/data/com.termux/files/usr/libexec/valgrind/vgpreload_memcheck-arm64-linux.so)
==22732==    by 0x5E875BF: exec_am_broadcast (termux-api.c:231)
==22732==
==22732== Syscall param execve(argv) points to uninitialised byte(s)
==22732==    at 0x5FEEB78: execve (in /apex/com.android.runtime/lib64/bionic/libc.so)
==22732==    by 0x5F18023: execve (in /data/data/com.termux/files/usr/lib/libtermux-exec.so)
==22732==  Address 0x6033e08 is 136 bytes inside a block of size 144 alloc'd
==22732==    at 0x5CC9FB4: malloc (in /data/data/com.termux/files/usr/libexec/valgrind/vgpreload_memcheck-arm64-linux.so)
==22732==    by 0x5E875BF: exec_am_broadcast (termux-api.c:231)
==22732==  Uninitialised value was created by a heap allocation
==22732==    at 0x5CC9FB4: malloc (in /data/data/com.termux/files/usr/libexec/valgrind/vgpreload_memcheck-arm64-linux.so)
==22732==    by 0x5E875BF: exec_am_broadcast (termux-api.c:231)

And fix a typo.

And prevent header from being included multiple times for no reason.

And link termux-api-broadcast against the static one to speed it up a
bit.

Suggested-by: @agnostic-apollo

…always using `TermuxAm` to send intents instead of the socket server that is run by the app

This is currently only done for Android `>= 14` and is a temporary patch until termux-app release is made with finalized support for termux-am-socket to send intents

Closes termux/termux-api#638, termux/termux-app#3754
Related termux/termux-app#3647, termux/TermuxAm@8b9844ab

…termux-api-broadcast` version