Compilation: enable PIE and PIC

[kewde]

For security reasons it's better to compile our code with position indepent code/execution, rendering the stack unexecutable protecting against buffer overflows.

LevelDB needs to be compiled with -fPIC
Shadow needs to be compiled with -e PIE=1

The makefile.unix in src specifies a way (scanelf) to check if a binary is compiled with non-executable stack.

[kewde]

All libraries we use need to be compiled with -fPIC.
The stack remains executable for the application if one library is not compiled as position independent.

I'm not statically compiling Shadow on my development environment so I can't make these edits for now.

fPIC list:

• LevelDB
• Boost
• Qt

Please note, this list is not exhaustive/complete.

Our main application is compiled with stack canaries which adds a layer of protection to our code, while this issue is not crucial, every bit helps.