Fix mp3lame builds on aarch64

[andreipoe]

On aarch64, the mp3lame build was failing to identify the system architecture as below:

*** Building mp3lame ***
checking build system type... ./config.guess: unable to guess system type

This script, last modified 2003-07-02, has failed to recognize
the operating system you are using. It is advised that you
download the most up to date version of the config scripts from

    ftp://ftp.gnu.org/pub/gnu/config/

If the version you run (./config.guess) is already up to date, please
send the following data and any information you think might be
pertinent to <config-patches@gnu.org> in order to provide the needed
information to handle your system.

config.guess timestamp = 2003-07-02

uname -m = aarch64
uname -r = 3.10.104-pine64
uname -s = Linux
uname -v = #2 SMP PREEMPT Thu Feb 23 22:26:21 CET 2017

/usr/bin/uname -p =
/bin/uname -X     =

hostinfo               =
/bin/universe          =
/usr/bin/arch -k       =
/bin/arch              =
/usr/bin/oslevel       =
/usr/convex/getsysinfo =

UNAME_MACHINE = aarch64
UNAME_RELEASE = 3.10.104-pine64
UNAME_SYSTEM  = Linux
UNAME_VERSION = #2 SMP PREEMPT Thu Feb 23 22:26:21 CET 2017
configure: error: cannot guess build type; you must specify one

Manually setting the target architecture by adding --build=arm-linux to ./configure fixes the problem.

[zimbatm]

Thanks!