The sequence of commands below assumes that you are patching Asterisk on an existing/working FreePBX Asterisk install, say from a distro. If doing the whole build newly from scratch, then you would need to follow these guidelines or these to ensure you have all the pre-requisites installed.
Make sure you are logged in as root.
Stop running Asterisk
amportal stop
Go to your src directory
cd /usr/src/
Download Asterisk 1.8.7.0
wget http://downloads.asterisk.org/pub/telephony/asterisk/releases/asterisk-1.8.7.0.tar.gz
Unpack it
tar zxvf asterisk-1.8.7.0.tar.gz
Change to the Asterisk source files directory you just unpacked
cd asterisk-1.8.7.0
Download mp3 support files
contrib/scripts/get_mp3_source.sh
Download the patch
wget https://issues.asterisk.org/jira/secure/attachment/41666/asterisk-1.8.7.0-chan_sip.patch
Apply the patch, as you are prompted, enter the path of the files as you go, per my post
patch -p0 < asterisk-1.8.7.0-chan_sip.patch
Optional: Remove the compiled binaries from within the source directory, there should not be any if this is the first time you have compiled the source code from this directory. If you subsequently recompile Asterisk from this directory then you will need to run this command
make clean
Run configure
./configure
Start menu based configuration
make menuconfig
select app_mysql, app_saycountpl, cdr_mysql, format_mp3, res_config_mysql
go to Extras Sound Packages
Select EXTRAS-SOUNDS-EN-GSM
Save & Exit
Run make
make
Run the installer
make install
Start running the newly patched Asterisk
amportal start