[Sound-open-firmware] SOF master build REMINDER

[Pan, Xiuli]

Reminder for applying this patch! On master branch

Please check if you have install 
sudo apt-get install autoconf-archive

And see this line when run ./autogen.sh

aclocal: installing 'm4/ax_check_compile_flag.m4' from '/usr/share/aclocal/ax_check_compile_flag.m4'

or have file
'm4/ax_check_compile_flag.m4'
in your git repo.

If not you will find these when configure.

./configure: line 3451: syntax error near unexpected token `-msse4.2,'
./configure: line 3451: `AX_CHECK_COMPILE_FLAG(-msse4.2, SSE42_CFLAGS="-DOPS_SSE42 -msse4.2 -ffast-math -ftree-vectorizer-verbose=0",'

It seems to be some m4 expand auto check about 'AX_CHECK_COMPILE_FLAG'. If you did no install this macro it will just copy but not expand it
in configure file. And then the error will occur.

Synced with Keqiao to update CI environment and build guide.

Thanks
Xiuli

>Subject: [Sound-open-firmware] [PATCH v5] build: add library build support for
>host platform
>
>This patch provides library build support for host platform architecture.
>It enables creating separate libraries for each SOF audio component.
>
>Signed-off-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>