Move falco engine to its own library.

Move the c++ and lua code implementing falco engine/falco common to its
own directory userspace/engine. It's compiled as a static library
libfalco_engine.a, and has its own CMakeLists.txt so it can be included
by other projects.

The engine's CMakeLists.txt has a add_subdirectory for the falco rules
directory, so including the engine also builds the rules.

The variables you need to set to use the engine's CMakeLists.txt are:

- CMAKE_INSTALL_PREFIX: the root directory below which everything is
  installed.
- FALCO_ETC_DIR: where to install the rules file.
- FALCO_SHARE_DIR: where to install lua code, relative to the
- install/package root.
- LUAJIT_INCLUDE: where to find header files for lua.
- FALCO_SINSP_LIBRARY: the library containing sinsp code. It will be
- considered a dependency of the engine.
- LPEG_LIB/LYAML_LIB/LIBYAML_LIB: locations for third-party libraries.
- FALCO_COMPONENT: if set, will be included as a part of any install()
  commands.

Instead of specifying /usr/share/falco in config_falco_*.h.in, use
CMAKE_INSTALL_PREFIX and FALCO_SHARE_DIR.

The lua code for the engine has also moved, so the two lua source
directories (userspace/engine/lua and userspace/falco/lua) need to be
available separately via falco_common, so make it an argument to
falco_common::init.

As a part of making it easy to include in another project, also clean up
LPEG build/defs. Modify build-lpeg to add a PREFIX argument to allow for
object files/libraries being in an alternate location, and when building
lpeg, put object files in a build/ subdirectory.

scripts/build-lpeg.sh

@@ -1,17 +1,29 @@
-#!/bin/sh
+#!/bin/bash
 
-gcc -O2 -fPIC -I$LUA_INCLUDE -c lpcap.c -o lpcap.o
-gcc -O2 -fPIC -I$LUA_INCLUDE -c lpcode.c -o lpcode.o
-gcc -O2 -fPIC -I$LUA_INCLUDE -c lpprint.c -o lpprint.o
-gcc -O2 -fPIC -I$LUA_INCLUDE -c lptree.c -o lptree.o
-gcc -O2 -fPIC -I$LUA_INCLUDE -c lpvm.c -o lpvm.o
+set -ex
+
+PREFIX=$1
+
+if [ -z $PREFIX ]; then
+    PREFIX=.
+fi
+
+mkdir -p $PREFIX
+
+gcc -O2 -fPIC -I$LUA_INCLUDE -c lpcap.c -o $PREFIX/lpcap.o
+gcc -O2 -fPIC -I$LUA_INCLUDE -c lpcode.c -o $PREFIX/lpcode.o
+gcc -O2 -fPIC -I$LUA_INCLUDE -c lpprint.c -o $PREFIX/lpprint.o
+gcc -O2 -fPIC -I$LUA_INCLUDE -c lptree.c -o $PREFIX/lptree.o
+gcc -O2 -fPIC -I$LUA_INCLUDE -c lpvm.c -o $PREFIX/lpvm.o
 
 
 # For building lpeg.so, which we don't need now that we're statically linking lpeg.a into falco
 #gcc -shared -o lpeg.so -L/usr/local/lib lpcap.o lpcode.o lpprint.o lptree.o lpvm.o
 #gcc -shared -o lpeg.so -L/usr/local/lib lpcap.o lpcode.o lpprint.o lptree.o lpvm.o
 
+pushd $PREFIX
 /usr/bin/ar cr lpeg.a lpcap.o lpcode.o lpprint.o lptree.o lpvm.o
 /usr/bin/ranlib lpeg.a
+popd
 
 chmod ug+w re.lua