$ tar -xzvf php-5.6.10.tar.gz
$ mv php-5.6.10 php
$ mkdir -p /Applications/MAMP/bin/php/php5.6.10/include
$ mv php /Applications/MAMP/bin/php/php5.6.10/include

$ cd /Applications/MAMP/bin/php/php5.6.10/include/php
$ ./configure

$ MACOSX_DEPLOYMENT_TARGET=10.10
$ CFLAGS="-arch i386 -arch x86_64 -g -Os -pipe -no-cpp-precomp"
$ CCFLAGS="-arch i386 -arch x86_64 -g -Os -pipe"
$ CXXFLAGS="-arch i386 -arch x86_64 -g -Os -pipe"
$ LDFLAGS="-arch i386 -arch x86_64 -bind_at_load"
$ export CFLAGS CXXFLAGS LDFLAGS CCFLAGS MACOSX_DEPLOYMENT_TARGET

$ cd ext/pcntl
$ phpize
$ ./configure
$ make
$ cp modules/pcntl.so /Applications/MAMP/bin/php/php5.6.10/lib/php/extensions/no-debug-non-zts-20131226/  

$ echo "extension=pcntl.so"  /Applications/MAMP/bin/php/php5.6.10/conf/php.ini

$ /Applications/MAMP/bin/php/php5.6.10/bin/php --ri pcntl
pcntl
pcntl support => enabled